Image decoding method and image decoding apparatus

ABSTRACT

An image decoding method for decoding a bitstream including a coded signal resulting from coding slices into which an image is partitioned and each of which includes coding units, includes decoding the coded signal, wherein each of the slices is either a normal slice having, in a slice header, information used for another slice or a dependent slice which is decoded using information included in a slice header of another slice, the image includes rows each of which includes coding units, and when the normal slice starts at a position other than the beginning of the first row, the second row immediately following the first row does not start with the dependent slice.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/705,864 filed on Sep. 26, 2012. The entire disclosureof the above-identified application, including the specification,drawings and claims is incorporated herein by reference in theirentirety.

FIELD

The present disclosure relates to an image coding method and an imagedecoding method.

BACKGROUND

At present, the majority of standardized video coding algorithms arebased on hybrid video coding. Hybrid video coding methods typicallycombine several different lossless and lossy compression schemes inorder to achieve the desired compression gain. The hybrid video codingis also the basis for ITU-T standards (H.26x standards such as H.261 andH.263) as well as ISO/IEC standards (MPEG-X standards such as MPEG-1,MPEG-2, and MPEG-4).

The most recent and advanced video coding standard is currently thestandard denoted as H.264/MPEG-4 advanced video coding (AVC) which is aresult of standardization efforts by Joint Video Team (JVT), a jointteam of ITU-T and ISO/IEC MPEG groups.

A video coding standard referred to as High-Efficiency Video Coding(HEVC) is also currently examined by Joint Collaborative Team on VideoCoding (JCT-VC) with the purpose of improving efficiency regarding thehigh-resolution video coding.

CITATION LIST Non Patent Literature

-   [Non Patent Literature 1] “Wavefront Parallel Processing for HEVC    Encoding and Decoding” by C. Gordon et al., no. JCTVC-F274-v2, from    the Meeting in Torino, July 2011-   [Non Patent Literature 2] “Tiles” by A. Fuldseth et al., no.    JCTVC-F355-v1, from the Meeting in Torino, July 2011 [Non Patent    Literature 3] JCTVC-J1003_d7, “High efficiency video coding (HEVC)    text specification draft 8” of July 2012

SUMMARY Technical Problem

In such image coding methods and image decoding methods, there has beena demand for improved efficiency in a situation where both parallelprocessing and dependent slices are used.

A non-limiting and exemplary embodiment provides an image coding methodand an image decoding method which make it possible to improve theefficiency of when the both parallel processing and dependent slices areused.

Solution to Problem

An image decoding method according to an embodiment of the presentdisclosure is an image decoding method for decoding a bitstreamincluding a coded signal resulting from coding a plurality of slicesinto which an image is partitioned and each of which includes aplurality of coding units, the method comprising decoding the codedsignal, wherein each of the slices is either a normal slice having, in aslice header, information used for another slice or a dependent slicewhich is decoded using information included in a slice header of anotherslice, the image includes a plurality of rows each of which includes towor more of the coding units, and when the normal slice starts at aposition other than a beginning of a first row, a second row immediatelyfollowing the first row does not start with the dependent slice.

These general and specific aspects may be implemented using a system, amethod, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, methods, integrated circuits, computer programs, orcomputer-readable recording media.

Further benefits and advantages of the disclosed embodiments will beapparent from the Specification and Drawings. These benefits andadvantages may be individually obtained by the various embodiments andfeatures of the Specification and Drawings, which need not always beprovided in order to obtain one or more of such benefits and/oradvantages.

Advantageous Effects

The present disclosure can provide an image coding method and an imagedecoding method which make it possible to improve the efficiency of whenboth parallel processing and dependent slices are used.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram showing an image coding apparatus according toembodiments.

FIG. 2 is a block diagram showing an image decoding apparatus accordingto the embodiments.

FIG. 3A is a schematic diagram for illustrating WPP according to theembodiments.

FIG. 3B is a schematic diagram for illustrating dependent slices in WPPaccording to the embodiments.

FIG. 4A is a schematic diagram for illustrating dependent slices whenWPP is not applied according to the embodiments.

FIG. 4B is a schematic diagram for illustrating dependent slices whenWPP is applied according to the embodiments.

FIG. 5 is a diagram showing a slice header of an entropy slice or adependent slice according to the embodiments.

FIG. 6 is a diagram showing an exemplary non-allowed slice structurewhen WPP is applied according to the embodiments.

FIG. 7 is a diagram showing an exemplary allowed slice structure whenWPP is applied according to the embodiments.

FIG. 8 is a schematic diagram showing a CABAC initialization processaccording to the embodiments.

FIG. 9 is a flow chart for a determination process in a CABACinitialization method for a dependent slice depending on characteristicsof a preceding slice according to the embodiments.

FIG. 10 is a diagram showing an exemplary slice structure according tothe embodiments.

FIG. 11 is a diagram showing an exemplary slice structure according tothe embodiments.

FIG. 12 is a diagram showing exemplary syntax of a slice headeraccording to Embodiment 1.

FIG. 13 is a flow chart for a determination process in a CABACinitialization method for a dependent slice according to Embodiment 1.

FIG. 14 is a diagram showing an exemplary picture partitioned intoslices according to Embodiment 2.

FIG. 15 is a flow chart for a determination process in a CABACinitialization method according to Embodiment 2.

FIG. 16 is a diagram showing an exemplary picture partitioned intoslices according to Embodiment 2.

FIG. 17A is a diagram showing an exemplary non-allowed slice structureaccording to Embodiment 2.

FIG. 17B is a diagram showing an exemplary allowed slice structureaccording to Embodiment 2.

FIG. 17C is a diagram showing an exemplary allowed slice structureaccording to Embodiment 2.

FIG. 17D is a diagram showing an exemplary allowed slice structureaccording to Embodiment 2.

FIG. 18 is a diagram showing an exemplary picture partitioned intoslices according to Embodiment 2.

FIG. 19 is a diagram showing an exemplary picture partitioned intoslices according to Embodiment 3.

FIG. 20 shows an overall configuration of a content providing system forimplementing content distribution services.

FIG. 21 shows an overall configuration of a digital broadcasting system.

FIG. 22 shows a block diagram illustrating an example of a configurationof a television.

FIG. 23 shows a block diagram illustrating an example of a configurationof an information reproducing/recording unit that reads and writesinformation from and on a recording medium that is an optical disk.

FIG. 24 shows an example of a configuration of a recording medium thatis an optical disk.

FIG. 25A shows an example of a cellular phone.

FIG. 25B shows a block diagram illustrating an example of aconfiguration of a cellular phone.

FIG. 26 illustrates a structure of multiplexed data.

FIG. 27 schematically shows how each stream is multiplexed inmultiplexed data.

FIG. 28 shows how a video stream is stored in a stream of PES packets inmore detail.

FIG. 29 shows a structure of TS packets and source packets in themultiplexed data.

FIG. 30 illustrates a data structure of a PMT.

FIG. 31 shows an internal structure of multiplexed data information.

FIG. 32 shows an internal structure of stream attribute information.

FIG. 33 shows steps for identifying video data.

FIG. 34 shows a block diagram illustrating an example of a configurationof an integrated circuit for implementing the moving picture codingmethod and the moving picture decoding method according to each ofembodiments.

FIG. 35 shows a configuration for switching between driving frequencies.

FIG. 36 shows steps for identifying video data and switching betweendriving frequencies.

FIG. 37 shows an example of a look-up table in which video datastandards are associated with driving frequencies.

FIG. 38A is a diagram showing an example of a configuration for sharinga module of a signal processing unit.

FIG. 38B is a diagram showing another example of a configuration forsharing a module of the signal processing unit.

DESCRIPTION OF EMBODIMENTS

(Underlying Knowledge Forming Basis of the Present Disclosure)

In relation to the image coding method and the image decoding methoddisclosed in the Background section, the inventors have found thefollowing problems.

First, an image coding apparatus and an image decoding apparatus in HEVCare described.

A video signal input to an image coding apparatus includes images eachreferred to as a frame (picture). Each frame includes pixels arranged ina two-dimensional matrix. In all the above-mentioned standards based onthe hybrid video coding, each individual frame is partitioned intoblocks each including pixels. The size of the blocks may vary, forinstance, in accordance with the content of an image. A different codingmethod may be used on a per block basis. For example, the largest sizeof the blocks is 64×64 pixels in HEVC. This largest size is referred toas a largest coding unit (LCU). The LCU can be recursively divided intofour coding units (CUs).

In H.264/MPEG-4 AVC, coding is performed on a per macroblock (usually16×16-pixel block) basis. There is a case where the macroblock isdivided into subblocks.

Typically, a coding step in hybrid video coding includes spatial and/ortemporal prediction. In short, each of current blocks to be coded ispredicted using blocks spatially or temporally adjacent to the currentblock, that is, coded video frames. Next, a residual block that is adifference between the current block and the prediction result iscalculated. Next, the residual block is transformed from spatial (pixel)domain to frequency domain. The transformation aims at reducingcorrelation of an input block.

Next, a transform coefficient resulting from the transformation isquantized. This quantization is lossy compression. Lossless compressionis performed on the quantization coefficient thus obtained, usingentropy coding. In addition, side information necessary forreconstructing the coded video signal is coded and output with the codedvideo signal. This information is, for instance, information aboutspatial prediction, temporal prediction, and/or quantization.

FIG. 1 is a block diagram showing an exemplary image coding apparatus100 compliant with H.264/MPEG-4 AVC and/or HEVC.

A subtractor 105 calculates a residual signal 106 (residual block) thatis a difference between a current block to be coded of an input imagesignal 101 and a corresponding prediction signal 181 (prediction block).The prediction signal 181 is generated by temporal prediction or spatialprediction by a prediction unit 180. A type of the prediction can bechanged on a per frame or block basis. A block and/or a frame predictedusing the temporal prediction is referred to as being inter-coded, and ablock and/or a frame predicted using the spatial prediction is referredto as being intra-coded.

A prediction signal used for the temporal prediction is derived using acoded and decoded image stored in a memory. A prediction signal used forthe spatial prediction is derived using boundary pixel values ofadjacent coded and decoded blocks stored in the memory. In addition, thenumber of intra-prediction directions is determined according to a sizeof coding units.

The residual signal 106 is also referred to as a prediction error or aprediction residual. A transformation unit 110 transforms the residualsignal 106 to generate a transformation coefficient 111. A quantizationunit 120 quantizes the transformation coefficient 111 to generate aquantization coefficient 121. An entropy coding unit 190 performsentropy coding on the quantization coefficient 121, with the purpose offurther reduction in an amount of data to be stored and losslesstransmission. For example, the entropy coding is variable-length coding.In addition, a length of a code word is determined based on aprobability of occurrence of a code.

A coded signal 191 (coded bitstream) is generated through the aboveprocessing.

The image coding apparatus 100 includes a decoding unit for obtaining adecoded image signal (reconstructed image signal). Specifically, aninverse transformation unit 130 performs inverse quantization andinverse transformation on the quantization coefficient 121 to generate aresidual signal 131. This residual signal 131 is, strictly speaking,different from the original residual signal 106 due to a quantizationerror also referred to as quantization noise.

Next, an adder 140 adds the residual signal 131 and the predictionsignal 181 to generate a decoded image signal 141. As stated above, tomaintain compatibility between the image coding apparatus and the imagedecoding apparatus, each of the image coding apparatus and the imagedecoding apparatus generates the prediction signal 181 using the codedand decoded image signal.

With the quantization, the quantization noise is superimposed on thedecoded image signal 141. The superimposed noise often differs for eachof blocks because coding is performed on a per block basis. With this,when especially strong quantization is performed, block boundaries ofthe decoded image signal become salient. Such blocking noise causesimage quality to appear degraded in human visual recognition. To reducethe blocking noise, a deblocking filter 150 performs deblocking filterprocessing on the decoded image signal 141.

For instance, in deblocking filter processing in H.264/MPEG-4 AVC,filter processing suitable for each of regions is selected for eachregion. For example, when blocking noise is large, a strong (narrowband)low-pass filter is used, and when blocking noise is small, a weak(broadband) low-pass filter is used. The intensity of the low-passfilter is determined according to the prediction signal 181 and theresidual signal 131. The deblocking filter processing smoothes edges ofblocks. With this, subjective image quality of the decoded image signalis enhanced. An image on which filter processing has been performed isused for motion-compensating prediction of the next image. Consequently,this filter processing reduces a prediction error, thereby making itpossible to improve coding efficiently.

An adaptive loop filter 160 performs sample adaptive offset processingand/or adaptive loop filter processing on a decoded image signal 151after the deblocking filter processing, to generate a decoded imagesignal 161. As above, the deblocking filter processing enhances thesubjective image quality. In contrast, the sample adaptive offset (SAO)processing and the adaptive loop filter (ALF) processing aim atincreasing reliability on a per pixel basis (objective quality).

The SAO is processing for adding an offset value to a pixel according toadjacent pixels. The ALF is used to compensate for image distortioncaused by compression. For instance, the ALF is a Wiener filter having afilter coefficient determined in a manner that a mean square error (MSE)between the decoded image signal 151 and the input image signal 101 isminimized. For example, a coefficient of the ALF is calculated andtransmitted on a per frame basis. Moreover, the ALF may be applied to anentire frame (image) or a local region (block). In addition, sideinformation indicating a region on which filter processing is to beperformed may be transmitted on a per block basis, frame basis, orquadtree basis.

To decode an inter-coded block, it is necessary that part of a coded andthen decoded image be stored in a reference frame buffer 170. Thereference frame buffer 170 holds the decoded image signal 161 as adecoded image signal 171. The prediction unit 180 performsinter-prediction using motion-compensating prediction. Specifically, amotion estimator first searches blocks included in a coded and decodedvideo frame for a block most similar to a current block. This similarblock is used as the prediction signal 181. A relative displacement(motion) between the current block and the similar block is transmittedas motion data to the image decoding apparatus. This motion data is, forinstance, three-dimensional motion vectors included in side informationprovided with coded video data. Here, the expression “three-dimensional”includes spatial two dimensions and temporal one dimension.

It is to be noted that to optimize prediction accuracy, a motion vectorhaving a spatial sub-pixel resolution such as a half pixel resolutionand a quarter pixel resolution may be used. The motion vector having thespatial sub-pixel resolution indicates a spatial location in a decodedframe where no pixel value exists, that is, a location of a subpixel.Thus, it is necessary to spatially interpolate a pixel value to performmotion-compensating prediction. This interpolation is performed by aninterpolation filter (included in the prediction unit 180 shown in FIG.1), for instance.

Both in the intra-coding mode and the inter-coding mode, thequantization coefficient 121 is generated by transforming and quantizingthe residual signal 106 that is the difference between the input imagesignal 101 and the prediction signal 181. Generally, the transformationunit 110 uses, for this transformation, an orthogonal transformationsuch as a two-dimensional discrete cosine transformation (DCT) orinteger version thereof. This efficiently reduces correlation of naturalvideo. In addition, a low-frequency component is generally moreimportant to image quality than a high-frequency component, and thusmore bits are used for the low-frequency component than for thehigh-frequency component.

The entropy coding unit 190 transforms a two-dimensional array of thequantization coefficient 121 into a one-dimensional array. Typically,so-called zigzag scanning is used for this transformation. In the zigzagscanning, a two-dimensional array is scanned in a predetermined orderfrom a DC coefficient at the left top corner of the two-dimensionalarray to an AC coefficient at the right bottom corner of the same.Energy normally concentrates in coefficients at the left upper part ofthe two-dimensional array which correspond to a low frequency, and thuswhen the zigzag scanning is performed, the latter values tend to bezero. With this, it is possible to achieve efficient coding by usingRun-length encoding as part of or pre-processing of the entropy coding.

In H.264/MPEG-4 AVC and HEVC, various types of the entropy coding areused. Although the fixed-length coding is performed on some syntaxelements, the variable-length coding is performed on most of the syntaxelements. In particular, context-adaptive variable-length coding isperformed on a prediction residual, and various other types of integercoding are performed on other syntax elements. In addition, there isalso a case where context-adaptive binary arithmetic coding (CABAC) isused.

The variable-length coding enables lossless compression of a codedbitstream. However, code words are of variable length, and thus it isnecessary to continuously decode the code words. In other words, beforea preceding code word is coded or decoded, a following code word cannotbe coded or decoded without restarting (initializing) the entropy codingor without separately indicating a location of the first code word(entry point) when decoding is performed.

A bit sequence is coded into one code word by arithmetic coding based ona predetermined probability model. The predetermined probability modelis determined based on content of a video sequence in the case of CABAC.Thus, the arithmetic coding and CABAC are performed more efficiently asa length of a bitstream to be coded is greater. To put it another way,the CABAC applied to the bit sequence is more efficient in a largerblock. The CABAC is restarted at the beginning of each sequence. Stateddifferently, the probability model is initialized at the beginning ofeach video sequence with a determined value or a predetermined value.

H.264/MPEG-4, H.264/MPEG-4 AVC, and HEVC include two functional layers,the video coding layer (VCL) and the network abstraction layer (NAL).The video coding layer provides a coding function. The NAL encapsulatesinformation elements into standard units referred to as NAL units,depending on a use such as transmission over a channel or storage into astorage device. The information elements are, for instance, codedprediction error signals and information necessary for decoding a videosignal. The information necessary for decoding a video signal is aprediction type, a quantization parameter, a motion vector, and so on.

Each of the NAL units can be classified into: a VCL NAL unit includingcompressed video data and related information; a non-VCL unitencapsulating additional data such as a parameter set relating to anentire video sequence; and supplemental enhancement information (SEI)for providing additional information usable for increasing decodingaccuracy.

For example, the non-VCL unit includes a parameter set. The parameterset refers to a set of parameters relating to coding and decoding of acertain video sequence. Examples of the parameter set include a sequenceparameter set (SPS) including parameters relating to coding and decodingof an entire video sequence (picture sequence).

The sequence parameter set has a syntax structure including syntaxelements. The picture parameter set (PPS) to be referred to is specifiedby pic_parameter_set_id, a syntax element included in each slice header.In addition, an SPS to be referred to is specified byseq_parameter_set_id, a syntax element included in the PPS. As above,the syntax elements included in the SPS are applied to the entire codedvideo sequence.

The PPS is a parameter set that defines parameters applied to coding anddecoding of one picture included in a video sequence. The PPS has asyntax structure including syntax elements. The picture parameter set(PPS) to be referred to is specified by pic_parameter_set_id, a syntaxelement included in each slice header. As above, the syntax elementsincluded in the SPS are applied to an entire coded picture.

Therefore, it is easier to keep track of the SPS than the PPS. This isbecause the PPS changes for each picture, whereas the SPS stays constantfor the entire video sequence that may last for several minutes orseveral hours.

A VPS is parameters in the highest layer, and includes informationrelating to video sequences. The information included in the VPS is abit rate, a temporal_layering structure of the video sequences, and soon. In addition, the VPS includes information about a dependency betweenlayers (dependency between different video sequences). As a result, theVPS can be considered as information about the video sequences, and anoutline of each of the video sequences can be obtained based on the VPS.

FIG. 2 is a block diagram showing an exemplary image decoding apparatus200 compliant with H.264/MPEG-4 AVC or HEVC video coding standard.

A coded signal 201 (bitstream) input to the image decoding apparatus 200is transmitted to an entropy decoding unit 290. The entropy decodingunit 290 decodes the coded signal 201 to obtain a quantizationcoefficient and information elements necessary for decoding such asmotion data and a prediction mode. In addition, the entropy decodingunit 290 inversely scans the obtained quantization coefficient with thepurpose of obtaining a two-dimensional array, to generate a quantizationcoefficient 291, and outputs the quantization coefficient 291 to aninverse transformation unit 230.

The inverse transformation unit 230 inversely quantizes and transformsthe quantization coefficient 291 to generate a residual signal 231. Theresidual signal 231 corresponds to a difference obtained by subtractinga prediction signal from an input image signal that has no quantizationnoise and error and is input to an image coding apparatus.

A prediction unit 280 generates a prediction signal 281 using temporalprediction or spatial prediction. Normally, decoded information elementsfurther include information such as a prediction type in the case of theintra-prediction, or information necessary for prediction such as motiondata in the case of the motion-compensating prediction.

An adder 240 adds the residual signal 231 in a spatial domain and theprediction signal 281 generated by the prediction unit 280, to generatea decoded image signal 241. A deblocking filter 250 performs deblockingfilter processing on the decoded image signal 241 to generate a decodedimage signal 251. An adaptive loop filter 260 performs sample adaptiveoffset processing and adaptive loop filter processing on the decodedimage signal 251, to generate a decoded image signal 261. The decodedimage signal 261 is output as a display image and stored as a decodedimage signal 271 in a reference frame buffer 270. The decoded imagesignal 271 is used for a subsequent block or temporal or spatialprediction of an image.

Compared to H.264/MPEG-4 AVC, HEVC has a function to assist advanceparallel processing of coding and decoding. As with H.264/MPEG-4 AVC,HEVC enables partitioning of a frame into slices. Here, each of theslices includes consecutive LCUs in a scanning order. In H.264/MPEG-4AVC, each slice is decodable, and spatial prediction is not performedbetween the slices. Thus, it is possible to perform the parallelprocessing on a per slice basis.

However, the slice has a considerably large header, and there is nodependency between the slices, thereby decreasing compressionefficiency. In addition, when the CABAC is performed on a small datablock, the efficiency of the CABAC coding is decreased.

In response to this, wavefront parallel processing (WPP) has beenproposed to allow more efficient parallel processing. In the WPP, aCABAC probability model for use in resetting the LCU which is locatedfirst (lead LCU) in each of LCU rows (hereinafter, simply also referredto as “rows”) of a picture is a probability model after the LCU which islocated second in a previous row is processed is used. This maintains adependency between blocks. Thus, it is possible to decode the LCU rowsin parallel. In addition, processing of each row is delayed by two LCUsrelative to the previous row.

Information indicating an entry point, a position at which decoding ofan LCU row is started, is signaled in a slice header. It is to be notedthat Non Patent Literature (NPL) 1 describes the details of the WPP.

A method for using a tile is available as another approach for enhancingparallelization. A frame (picture) is partitioned into tiles. Each ofthe tiles is rectangular and includes LCUs. Boundaries between the tilesare set to partition the picture into matrices. In addition, the tilesare processed in a raster scanning order.

All dependencies are lost at the boundary of each tile. The entropycoding such as the CABAC is reset at the beginning of the tile. It is tobe noted that only the deblocking filter processing and the sampleadaptive offset processing are applied over the boundaries between thetiles. Thus, it is possible to code or decode the tiles in parallel. Itis to be noted that NPL 2 and NPL 3 describe the details of the tiles.

Moreover, the concept of dependent slices and entropy slices has beenproposed to make the concept of slices suitable for parallelizationrather than for error resilience which was the original purpose ofslices in H.264/MPEG-4 AVC. In other words, the following three types ofslices are used in HEVC: a normal slice, a dependent slice, and anentropy slice.

The normal slice is a slice already known from H.264/MPEG-4 AVC. Thespatial prediction cannot be performed between normal slices. In short,prediction cannot be performed over boundaries between slices. To put itanother way, the normal slice is coded without referring to anotherslice. The CABAC is restarted at the beginning of each slice to allowseparate decoding of the slice.

The normal slice is used for the beginning of a frame. Stateddifferently, each frame must start from the normal slice. The normalslice has a header including parameters necessary for decoding slicedata.

The entropy slice is a slice that enables the spatial prediction betweena parent slice and the entropy slice, for instance. Here, the parentslice is a normal slice immediately preceding the entropy slice. Theparent slice and the entropy slice are parsed independently.

The slice data is parsed independently of the parent slice and theentropy slice except syntax elements of a slice header. In other words,CABAC decoding of the entropy slice requires syntax elements included ina slice header of the parent slice. For example, the syntax elementsinclude switch information indicating whether the slice data includesfiltering parameters. When the slice data includes the filteringparameters, a CABAC decoding unit extracts the switch information.Otherwise, the CABAC decoding unit does not assume filtering data. Toput it another way, after parsing a slice header of the normal slice,the CABAC decoding unit is capable of processing the parent slice andthe entropy slice in parallel.

However, the parent slice may be, for instance, the normal slice, and isrequired for reconstructing pixel values of the entropy slice. Inaddition, the CABAC is restarted at the beginning of the slice to allowthe independent parsing of the entropy slice.

A slice header shorter than the slice header of the normal slice can beused for the entropy slice. The slice header includes a coding parametersubset regarding information transmitted within the slice header of thenormal slice. Information not included in the slice header of theentropy slice is copied from the slice header of the parent slice.

The dependent slice is similar to an entropy slice for which the CABACis not restarted. The restarting of the CABAC includes an initializingprocess in which a context table (probability table) is initialized to adefault value, and a termination process (terminate process) in thearithmetic coding or arithmetic decoding.

The slice header of the parent slice is used to parse and/or decode thedependent slice. Since the dependent slice cannot be parsed without theparent slice, the dependent slice cannot be decoded when the parentslice is not obtained. The parent slice is usually a slice preceding thedependent slice in coding order and including a complete slice header.The same holds true for a parent slice of the entropy slice.

Generally, the entropy slice can be considered as depending on headerparameters of another slice, and thus the present disclosure can beapplied to both the dependent slice and the entropy slice.

As described above, the dependent slice and the entropy slice use theslice header (the information not included in the slice header of thedependent slice) of the immediately preceding slice in coding order ofthe slices. This rule is recursively applied. It is recognized that aparent slice on which a target dependent slice depends is referable.Referring includes use of the spatial prediction between slices, acommon CABAC state, and so on. The dependent slice uses a CABAC contexttable generated at the end of the immediately preceding slice. In thisway, the dependent slice continuously uses the generated table withoutinitializing a CABAC table to a default value. NPL 3 describes theentropy slice and the dependent slice (see “dependent_slice_flag” onpage 73, for instance).

In the case of using the WPP, when a dependent slice starts at thebeginning of an LCU row and a slice including an LCU located to theupper right of the beginning of the LCU row is indicated as beingreferable, the dependent slice uses a CABAC context table of the LCU.

HEVC presents several profiles. A profile includes settings of an imagecoding apparatus and an image decoding apparatus suitable for aparticular application. For instance, a “main profile” includes onlynormal slices and dependent slices, but not entropy slices.

As stated above, a coded slice is encapsulated into a NAL unit, furtherencapsulated into, for example, a real time protocol (RTP), and finallyencapsulated into an internet protocol (IP) packet. This protocol stackor another protocol stack allows transmission of coded video in theInternet or a packet-oriented network such as a proprietary network.

Typically, a network includes at least one router, and the routerincludes dedicated hardware that operates at ultrahigh speed. The routerreceives IP packets, parses their headers, and appropriately forwardsthe IP packets to their respective destinations. The router is requiredto process communication from many sources, and thus packets thatcontrol logic must be as simple as possible. The router at least needsto check destination address fields included in the IP headers, todetermine paths through which the IP packets are forwarded. A smart(media-aware) router additionally checks dedicated fields in networkprotocol headers such as the IP headers, RTP headers, and NALU headers,to further provide support for the quality of service (QoS).

As is clear from the above description of the video coding, thedifferent types of slices defined for the parallel processing such asthe dependent slice and the entropy slice differ in significance forimage degradation when data are lost. The dependent slice cannot beparsed and decoded without the parent slice. This is because an entropycoding unit or an entropy decoding unit cannot be restarted at thebeginning of the dependent slice. Thus, the parent slice can be said tobe more important in reconstructing an image or video than the parentslice.

In HEVC, the dependent slice and the entropy slice have a dependencybetween slices (dependency within a frame) as an additional aspect ofthe dependency. This dependency is not the only dependency within theframe.

Since parallel processing of slices is performed for each tile, contextsof an arithmetic coding unit and an arithmetic decoding unit aredetermined by default settings or coded or decoded slices. However, adependency of a header and a dependency of arithmetic codinginitialization are different from each other, and thus there is apossibility of delay or further complexity in contradiction to thepurposes of the parallel processing and a dependent slice mechanism.

The dependent slice can be used in conjunction with a parallelprocessing tool such as the WPP and tiles. In addition, a wavefront(substream) that makes it possible to reduce transmission delay withoutcausing coding loss can be generated using the dependent slice.

The CABAC is not restarted for the dependent slice, and thus thedependent slice can be used as an entry point of a CABAC substream. Inaddition, to indicate an entry point for independent parsing,information indicating the entry point may be signaled in a bitstream.In particular, when two or more CABAC substreams are encapsulated into anormal slice or a dependent slice, an entry point is signaled explicitlyusing the number of bytes for each substream. Here, the substreamindicates a portion of a stream separately parsable based on the entrypoint. Moreover, each dependent slice requires a header of a NAL unit,and thus the dependent slice can be used as a “marker” of an entrypoint. In short, the entry point corresponding to such a marker can besignaled.

It is possible to simultaneously use a method for explicitly signalingan entry point and a method for marking an entry point through adependent slice. Here, there is a need to identify an entry point ofeach NAL unit (beginning of each NAL header). It is to be noted that anymethod can be used for the identification method. For example, thefollowing two methods can be used.

The first method is inserting a start code of 3 bytes at the beginningof each NAL header, for instance. The second method is packetizing eachNAL unit into a different packet. In addition, a size of a slice headermay be reduced due to the dependency of the slice.

These methods allow parallel CABAC parsing of an entropy slice. This isbecause the CABAC is always restarted at the beginning of the entropyslice. In parallel processing of the CABAC, a bottleneck can be overcomeby the parallel CABAC parsing after consecutive pixel reconstructionprocessing. Specifically, with a WPP parallelization tool, decoding ofeach LCU row can be achieved by one processing core. It is to be notedthat different LCU rows may be assigned to respective cores. Forexample, two rows may be assigned to one core, or one row may beassigned to two cores.

FIG. 3A is a diagram showing a picture 300 partitioned into rows. Eachof the rows includes largest coding units (LCUs). A row 301(Wavefront 1) and a row 302 (Wavefront 2) are processed in parallel. Asshown by an arrow of CABAC states in FIG. 3A, after the first two LCUsare decoded in the row 301, processing of the row 302 is started. Inaddition, CABAC states after the first two LCUs of the row 301 are codedor decoded are used for CABAC initialization of the row 302. Thus, theprocessing of the row 302 can be started after the processing of thefirst two LCUs of the row 301 is finished. In short, the delay of thetwo LCUs exists between the two processing cores.

FIG. 3B is a diagram showing a usage example of dependent slices for theWPP. A picture 310 shown in FIG. 3B includes rows 311 to 314. Here, therow 311 (Wavefront 1), the row 312 (Wavefront 2), and the row 313(Wavefront 3) are processed using separate cores.

The dependent slices allow the WPP that is capable of reducing delay.The dependent slices have no complete slice header. Moreover, when entrypoints (the entry points of the dependent slices which are known for theabove rule) are known, the dependent slices can be decoded independentlyof other slices. Furthermore, the dependent slices allow the WPPsuitable for low delay applications without causing coding loss.

In a normal case where a substream (LCU row) is encapsulated into aslice, it is necessary to insert a clear entry point into a slice headerto surely perform entropy coding and entropy decoding in parallel. Forthis reason, transmission of the slice can be prepared only after thelast substream of the slice is completely coded. In addition, the sliceheader is completed only after coding of all substreams in the slice isfinished. In other words, transmission of the beginning of the slicecannot be started through packet fragmentation in the RTP/IP layer untilprocessing of the whole slice is finished.

However, when a dependent slice is used, the dependent slice can be usedas an entry point marker, and thus it is not necessary to performnotification using an explicit signal of an entry point. Consequently,it is possible to split a normal slice into many dependent sliceswithout coding loss. In addition, the dependent slices can betransmitted immediately after coding of the encapsulated substream isfinished (or before the coding in the case of the packet fragmentation).

The dependent slices do not decrease a spatial prediction dependency. Inaddition, the dependent slices do not decrease a parsing dependency.This is because parsing of a target dependent slice normally requiresCABAC states of a preceding slice.

When the dependent slice is not allowed, each LCU row can be used as aslice. Although such a configuration reduces the transmission delay,significant coding loss is caused simultaneously as stated above.

The following assumes a case where a whole frame (picture) isencapsulated into one slice. In this case, to make parallel parsingpossible, it is necessary to signal, in a slice header, an entry pointof a substream (LCU row). This causes a transmission delay at a framelevel. To put it another way, it is necessary to modify the header afterthe whole frame is coded. The encapsulation of the whole picture intothe one slice itself does not worsen the transmission delay. Forinstance, transmission of part of the slice may be started before thecoding is completely finished. However, when the WPP is used, it isnecessary to modify the slice header later to indicate the entry point.Thus, it is necessary to delay the transmission of the whole slice.

As above, the usage of the dependent slice makes it possible to reducethe delay. As shown in FIG. 3B, the picture 310 is partitioned into therow 311, a normal slice, and the rows 312, 313, and 314, dependentslices. When each row is one dependent slice, it is possible to delaytransmission of the one row without coding loss. This is because thedependent slice does not decrease the spatial dependency and does notrestart a CABAC engine.

FIG. 4A and FIG. 4B each are a diagram showing another example of CABACinitialization. FIG. 4A shows the CABAC initialization when the WPP isnot used. The WPP and tiles are both unused. The usage of the normalslices and the dependent slices together is allowed.

A dependent slice (3) copies the header of a normal slice (2). In short,the normal slice (2) is a parent slice of the dependent slice (3). Thedependent slice (3) uses a context table generated at the end of thenormal slice (2). The dependent slice (3) depends not on a normal slice(1) but on the normal slice (2). In a word, spatial prediction does notexist between the normal slice (1) and the dependent slice (3).

FIG. 4B is a diagram showing the CABAC initialization when the WPP isused. The usage of the normal slices, the dependent slices, and the WPPtogether is allowed.

A dependent slice (3) copies the header of a normal slice (2). Thedependent slice (3) is expected to use a context table generated at theend of the LCU located second in the normal slice (1). However, sincethe slice (2) is a normal slice, it is indicated that the LCU locatedsecond in the slice (1) cannot be referred to. In short, the slice (1)is not referred to, because the slice (1) is not an immediatelypreceding slice of a dependent slice in coding order.

However, the slice (2) is used as a reference slice for the slice (3)and a slice (4). In other words, when decoding of the slice (3) isstarted, it is necessary to initialize CABAC states to a default value(indicated by a dashed arrow in FIG. 4B). The dependent slice (4) usesCABAC states (solid arrow) after the right upper second LCU whichconforms to the above-mentioned WPP conditions.

FIG. 5 is a diagram showing an exemplary syntax of a slice headercompliant with a current HEVC reference model (HM8.0). A slice header320 includes a syntax element dependent slice_flag which indicateswhether a target slice is a dependent slice or a normal slice.

As is clear from a row 321 in FIG. 5, when the dependent_slice_flag isequal to 0, the header has slice header information. In short, the slicehas a complete header. Otherwise, the header does not have the sliceheader information. To put it another way, as above, the dependent sliceand an entropy slice have no complete slide header, and refer to theheader of a preceding normal slice.

Entry points are signaled later to support parallel processing. Evenwhen the entropy coding unit or the entropy decoding unit is notrestarted, it is possible to independently perform parallel decoding ofpart of a video stream (substream) between the entry points, using theentry points. As stated above, entry points are marked for the dependentslice, the normal slice, and the entropy slice.

In HEVC, several parallel processing tools are available. As mentionedabove, the tools include the WPP, the dependent slice, the entropyslice, and the tile. However, since these tools are not compatible witheach other, there is a limit to combined usage of the tools. The usageof the tile and the slice together is generally allowed.

However, there is a restriction that in a major profile, one slice needsto be subdivided into an integer number of tiles greater than or equalto 1, and one tile needs to be subdivided into an integer number ofslices greater than or equal to 1. This restriction is typically appliedto a specific profile (or a specific level of a profile). The purpose ofthe restriction is to reduce complexity of hardware implementation.

When entropy_coding_sync_enabled_flag of a PPS is equal to 1 (i.e., theWPP is used), and the coding block located first in a slice is not thecoding block located first in the coding tree block located first in arow of coding tree blocks in a tile, a condition under which a bitstreammeets standards is that the last coding block in the slice belongs tothe same row of the coding tree blocks as the coding block located firstin the slice. A coding tree indicates a structure of an LCU andrecursive further subdivision of each of LCUs into four blocks. Stateddifferently, when the WPP can be used, and the slice does not start atthe beginning of a target LCU row, the slice has to end at or before theend of the target LCU row. NPL 3 describes details regarding not onlyparallel processing means but also HEVC syntax.

The following describes this restriction with reference to FIG. 6. Apicture 330 shown in FIG. 6 includes slices 331, 332, and 333, normalslices. The slices 331 and 332 are included in one LCU row. The slice333 is a non-allowed slice, because the slice 333 extends over LCU rows(three rows in this example). The slice 333 has to end at the end of thefirst LCU row in accordance with the above restriction.

FIG. 7 is a diagram showing a picture 340 having an allowed slicestructure when the WPP is used. The picture 340 includes slices 341,342, and 343, normal slices, and a slice 344, a dependent slice. Theslices 341, 342, and 343 are included in the first LCU row. The slice344 includes subsequent two rows.

The CABAC initialization of the slice 344 depends on the other slices341, 342, and/or 343, because the slice 344 is the dependent slice. Whenany of the slices 342 and 343 is a normal slice as shown in FIG. 7, theslice 344 is initialized to default CABAC states. Otherwise, a WPP tableis used. In other words, CABAC states after the LCU located second in anLCU row above a target row is processed are used for the initialization.

In this example, as described in FIG. 4B and stated in the relateddescription of the CABAC initialization, the CABAC initialization of thedependent slice 344 is performed using predetermined default CABACstates.

Thus, the CABAC initialization is based on preceding slices. Thus,processing, especially parsing, of a target slice depends on otherslices. Specifically, it is determined whether a CABAC context isinitialized with a default value or a WPP value depending on a type ofthe preceding slices of the target slice. In this way, it is checkedwhether or not the preceding slices can be used, and an initializationmethod to be applied to the target slice is determined. In short,processing having a quite complicated order is required. The followingdescribes such processing.

A first slice 341 has at least two LCUs, and thus CABAC states after thefirst two LCUs are coded or decoded can be referred to.

When a slice 342 or a slice 343 is lost, the slice 344 cannot beaccurately decoded. This is because the CABAC initialization cannot beperformed due to an unknown type of the slice 342 or the slice 343. Inother words, because the CABAC initialization cannot be performed on theslice 344 even when only information about the two preceding slices isabsent and the slice 344 has been correctly obtained, data of thecorrectly obtained slice 344 is discarded. Thus, it is necessary toperform error concealment on the slice 344. From this reason, there is apossibility that image degradation results from distortion due toincomplete error concealment.

Here, in a slice header, most of syntax elements (these are mainlyswitching of control such as a specific filtering operation) need to bedetermined for all slices included in a frame. In addition, althoughsome of the syntax elements can be changed on a slice basis, all controlparameters determined for a whole frame are held in most of processes byan image coding apparatus. Thus, the following method can be used as anerror concealment method. This method requires only informationindicating whether a lost slice is a dependent slice or a normal slice.

When packets arrive not in order, a decoding delay increases. In otherwords, when packet reordering is expected, there is a possibility ofincreasing the decoding delay. This contradicts with providing an ultralow delay using a dependent slice, the fundamental aim of the WPP.

FIG. 8 is a diagram showing another example of the CABAC initializationprocess. In FIG. 8, the structure of the slices shown in FIG. 7 isassumed. A picture 350 shown in FIG. 8 includes a slice 351 and a slice354. The slice 351 is a normal slice and located first in a frame, andincludes four LCUs. The CABAC is initialized to a default state value(zero state) at the beginning of the frame, that is, the beginning ofthe slice 351. It is to be noted that default states may be present, andin this case, one of the default states is selected. Here, the defaultstate refers to a predetermined value in a probability model ofarithmetic coding.

When data of the slice 342 and the slice 343 (see FIG. 7) are absent dueto missing or an error although data belonging to a dependent slice 354is obtained, the dependent slice 354 cannot be decoded. This is because,as stated above, the CABAC engine cannot be initialized without the dataof the slices 342 and 343.

FIG. 9 is a flow chart for a determination process in an initializationmethod which is performed when the dependent slice 354 is obtained. Toput it another way, this flow chart shows a method of depending on twoor more slices in the CABAC initialization.

It is assumed that the following conditions are set for a slice (4)(dependent slice 354). The WPP can be used. dependent_slice_enabled_flagof an SPS is set to 1. The position of the slice (4) satisfiesExpression 1.slice_address % numLCUinRow=0  (Expression 1)

Here, “%” represents a modulo operation (remainder of integer division).The parameter numLCUinRow represents the number of LCUs per row of thepicture 350. Thus, the condition of Expression 1 is satisfied at thebeginning of the row. The parameter numLCUinRow can be derived from thesettings of the SPS.

First, it is determined whether or not the slice (4) is a dependentslice (S101). When the slice (4) is not a dependent slice (No in S101),default initialization is performed.

As shown in FIG. 8, when the slice (4) is a dependent slice (Yes inS101), i is set to 3 (S102). In short, the slice (3) immediatelypreceding the slice (4) is set as a slice i.

Next, it is determined whether or not the slice i starts from a rowabove a row of the slice (4) (S103). Here, since i is set to 3, theslice i is the slice (3) immediately preceding a dependent slice to beprocessed (slice (4)).

When the slice i does not start from the row above the row of the slice(4) (No in S103), WPP initialization (initialization using a WPP table)is performed (S107).

In contrast, when the slice i starts from the row above the row of theslice (4) (Yes in S103), that is, in the case shown in FIG. 8, it isdetermined whether or not the slice i is a dependent slice (S104).

When the slice i is not a dependent slice (No in S104), a start positionof the slice i is then analyzed. Specifically, it is determined whetheror not slice_address % numLCUinRow is less than 2 (S106). In short, itis determined whether the start position of the slice i is the first LCUor the second LCU in the row.

When slice_address % numLCUinRow is less than 2 (Yes in S106), the WPPinitialization is performed (S107). In contrast, when slice_address %numLCUinRow is greater than or equal to 2 (No in S106), the defaultinitialization is performed (S108).

Moreover, when the slice i is a dependent slice (Yes in S104), a startposition of the slice i is analyzed. Specifically, it is determinedwhether or not slice_address ° A) numLCUinRow is less than 3 (S105). Inshort, it is determined whether the start position of the slice i is theLCU located first, second, or third in the row.

When slice_address % numLCUinRow is less than 3 (Yes in S105), the WPPinitialization is performed (S107). In contrast, when slice_address %numLCUinRow is greater than or equal to 3 (No in S105), theinitialization is not performed, and the index i is decreased by 1(S109). In short, in this example, the slice (2) preceding the targetslice (slice (4)) by two slices is set as the slice i. Then, theprocesses subsequent to step S103 are performed on the slice (2).Moreover, when the same determination is made for the slice (2), theslice (1) is then set as the slice i.

FIG. 10 is a diagram showing a picture 360. The picture 360 includesfive slices 361 to 365. The slice 361 is a normal slice and includes thewhole first row. The slice 362 is a dependent slice and includes thewhole second row. The third row includes the dependent slice 363 and theslice 364. The slice 365 is a dependent slice and includes the wholefourth row.

The following discusses cases where the slice 364 is a dependent sliceand where the slice 364 is a normal slice when the slice 364 is lost ordelayed. In addition, here, the slice 363 has at least two LCUs.

When the slice 364 is lost, an image decoding apparatus cannot determinea type of the slice 364. When the lost slice 364 is a dependent slice,it is possible to continue decoding of the slice 365 and subsequentslices with a small margin of error in reconstruction processing. Thisis because, as described with reference to FIGS. 8 and 9, the slice 365uses CABAC states of the LCU located second in the slice 363. Thus, theCABAC initialization processing causes no error. However, since theslice 365 uses spatial prediction from the slice 364, there is apossibility that the pixel reconstruction processing causes an error.

In contrast, when the lost slice 364 is a normal slice, the slice 365cannot be decoded. This is because some of syntax elements might useinformation of a slice header of the lost slice 364. Stated differently,it is because the normal slice 364 is a parent slice of the dependentslice 365, and the information of the parent slice is required forparsing and decoding of the dependent slice 365.

When the type of the lost slice 364 is unknown, the image decodingapparatus discards the decodable slice 365 to avoid wrong decoding thatis likely to occur when the lost slice 364 is a normal slice. This isinefficient because the slice 365 is discarded even when the data of theslice 365 is correctly obtained. In addition, it is necessary to discardall dependent slices subsequent to the slice 365.

When the slice 364 is a normal slice, a CABAC engine is initialized to adefault CABAC value (refer to the case of No in S101 in FIG. 9) todecode the slice 365. Thus, the slice 365 does not depend on the slice363. In addition, spatial prediction between the slice 363 and the slice365 is not performed. As above, the CABAC is initialized to the defaultvalue at the start position of the slice 365, and thus the dependentslice 365 becomes similar to the normal slice.

However, the normal slice has a complete slice header. In contrast, theslice 365 has only a short slice header and depends on parameters set bya slice header of a preceding normal slice. In other words, when theslice 365 is a dependent slice, although there is the advantage that thesize of the header can be reduced, the advantage is not so great. Incontrast, when the slice 365 is a normal slice, the slice 365 can bedecoded. As just described, in the above cases, the advantage isconsidered to be greater when the slice 365 is set as the normal slicethan when the slice 365 is set as the dependent slice.

However, in the WPP, the dependent slice is designed not to ensurerobustness against loss but to enable a WPP operation at an ultra lowdelay. On the other hand, in the case of an ultra low delay applicationover a network such as a real-time application, packet loss and packetreordering are expected. In such a case, when the slice 364 can befinally obtained, the slice 365 can be decoded. However, at least anincreased delay and the packet loss are caused. Thus, the WPP isperformed not in an optimum state in a lossy environment.

FIG. 11 is a diagram showing another problem associated with the CABACinitialization when the WPP is used, and showing a picture 370. Thepicture 370 includes four slices 371 to 374.

The slice 371 is a normal slice, and the slice 372 is a dependent slice.Here, the slice 371 has at least two LCUs. The first row of the picture370 includes the slices 371 and 372. The second row of the picture 370includes the slices 373 and 374, dependent slices.

In this case, an image coding apparatus is assumed to use at least twoprocessor cores. To put it another way, when the WPP is used, the imagecoding apparatus codes and parses two LCU rows in parallel. Thus, theslice 373 becomes available long before the slice 372 becomes available.

However, since the CABAC initialization for the slice 373 depends on theslice 372, decoding of the slice 373 cannot be started. Thus, it is notpossible to make a delay of starting coding or decoding between rowssmaller than entire one LCU row. This contradicts with the WPP's purposeof decreasing the delay up to two LCUs.

The following describes parallel processing of coding and transmitting aslice, as shown in FIG. 11. Two processing units such as processor coresand processors simultaneously code the slices (slice 371 and slice 373)located first in respective rows. When the coding ends, the coded slices371 and 373 are encapsulated into packets having packet numbers(packet_id) of 0 and 4, respectively. Here, the packet number of 4 isselected to reserve a small number for the slice 372 and possibly foranother NALU.

When coding of the slice 372 is completed, the slice 372 is encapsulatedinto a packet having a packet number of 1 and is transmitted. Inaddition, two NAL units having corresponding packet numbers of 2 and 3and dummy (filler) data are generated to avoid determination of lostpacket numbers of 2 and 3 as packet loss.

In HEVC, this is achieved by using a filler_data SEI message or apredetermined NAL unit type reserved for filler data. As above, when apacket ID needs to be increased by 1 for each NAL unit, a filler typeNALU is used to fill the gap.

Initialization of a target row depends on the LCU located second in arow above the target row. Moreover, a slice insertion after the LCUlocated second is problematic in terms of influencing the determinationof the CABAC initialization. The present disclosure provides a methodfor deriving a more efficient relationship between WPP and usage of adependent slice, based on this analysis and problem. A situation shouldbe avoided where the CABAC initialization for one row depends on anotherrow to maintain efficiency of the WPP.

An image decoding method according to an embodiment of the presentdisclosure is an image decoding method for decoding a bitstreamincluding a coded signal resulting from coding a plurality of slicesinto which an image is partitioned and each of which includes aplurality of coding units, the method comprising decoding the codedsignal, wherein each of the slices is either a normal slice having, in aslice header, information used for another slice or a dependent slicewhich is decoded using information included in a slice header of anotherslice, the image includes a plurality of rows each of which includes towor more of the coding units, and when the normal slice starts at aposition other than a beginning of a first row, a second row immediatelyfollowing the first row does not start with the dependent slice.

With this, it is possible to prevent an occurrence of a case where aslice at the beginning of the second row refers to a slice at a positionother than the beginning of the first row, thereby allowing improvedefficiency of when parallel processing and dependent slices are usedtogether.

For example, in the decoding, it may be that the first row and thesecond row are decoded in parallel, and when the decoding of the secondrow is started, the second row is decoded without referring to partitioninformation indicating a slice structure of the first row.

For example, in the decoding, arithmetic decoding of the second row maybe initialized using a context obtained after arithmetic decoding of oneof the coding units that is located second in the first row.

For example, the image decoding method may further comprise obtaining,from a slice header of a slice, information indicating whether the sliceis either the normal slice or the dependent slice.

For example, it may be that a slice at a beginning of the image is thenormal slice, and each of all other slices is the dependent slice.

For example, each of the slices may include an entirety of one or moreof the rows.

For example, arithmetic decoding of the dependent slice may beinitialized using a context of a parent slice whose slice header is usedfor the dependent slice.

For example, the image decoding method may further comprise obtaining arestriction indicator from the bitstream when the dependent slice isenabled, the restriction indicator indicating that partitioning of apicture is restricted.

Furthermore, an image coding method according to an embodiment of thepresent disclosure is an image coding method for coding a plurality ofslices into which an image is partitioned and each of which includes aplurality of coding units, to generate a bitstream, the methodcomprising: partitioning the image into the slices; and coding theslices resulting from the partitioning, wherein

each of the slices is either a normal slice having, in a slice header,information used for another slice or a dependent slice which is decodedusing information included in a slice header of another slice, the imageincludes a plurality of rows each of which includes two or more of thecoding units, and in the partitioning, when the normal slice starts at aposition other than a beginning of a first row, the image is partitionedinto the slices to cause a second row immediately following the firstrow to not start with the dependent slice.

With this, it is possible to prevent an occurrence of a case where aslice at the beginning of the second row refers to a slice at a positionother than the beginning of the first row, thereby allowing improvedefficiency of when parallel processing and dependent slices are usedtogether.

For example, in the partitioning, it may be that, in the case where animage decoding apparatus decodes the first row and the second row inparallel, the image is partitioned into the slices to allow the decodingof the second row without referring to partition information when theimage decoding apparatus starts decoding the second row, the partitioninformation indicating a slice structure of the first row.

For example, in the coding, arithmetic coding of the second row may beinitialized using a context obtained after arithmetic coding of one ofthe coding units that is located second in the first row.

For example, the image coding method may further comprise

embedding, into a slice header of a slice, information indicatingwhether the slice is either the normal slice or the dependent slice.

For example, it may be that a slice at a beginning of the image is thenormal slice, and each of all other slices is the dependent slice.

For example, each of the slices may include an entirety of one or moreof the rows.

For example, arithmetic coding of the dependent slice may be initializedusing a context of a parent slice whose slice header is used for thedependent slice.

For example, the image coding method may further comprise

embedding a restriction indicator into the bitstream when the dependentslice is enabled, the restriction indicator indicating that partitioningof a picture is restricted.

Furthermore, an image decoding apparatus according to an embodiment ofthe present disclosure is an image decoding apparatus which decodes abitstream including a coded signal resulting from coding a plurality ofslices into which an image is partitioned and each of which includes aplurality of coding units, the apparatus comprising a decoding unitconfigured to decode the coded signal, wherein each of the slices iseither a normal slice having, in a slice header, information used foranother slice or a dependent slice which is decoded using informationincluded in a slice header of another slice, the image includes aplurality of rows each of which includes two or more of the codingunits, and when the normal slice starts at a position other than abeginning of a first row, a second row immediately following the firstrow does not start with the dependent slice.

With this, it is possible to prevent an occurrence of a case where aslice at the beginning of the second row refers to a slice at a positionother than the beginning of the first row, thereby allowing improvedefficiency of when parallel processing and dependent slices are usedtogether.

Furthermore, an image coding apparatus according to an embodiment of thepresent disclosure is an image coding apparatus which codes a pluralityof slices into which an image is partitioned and each of which includesa plurality of coding units, to generate a bitstream, the apparatuscomprising: a partitioning unit configured to partition the image intothe slices; and a coding unit configured to code the slices resultingfrom the partitioning, wherein each of the slices is either a normalslice having, in a slice header, information used for another slice or adependent slice which is decoded using information included in a sliceheader of another slice, the image includes a plurality of rows each ofwhich includes two or more of the coding units, and the partitioningunit is configured to, when the normal slice starts at a position otherthan a beginning of a first row, partition the image into the slices tocause a second row immediately following the first row to not start withthe dependent slice.

With this, it is possible to prevent an occurrence of a case where aslice at the beginning of the second row refers to a slice at a positionother than the beginning of the first row, thereby allowing improvedefficiency of when parallel processing and dependent slices are usedtogether.

Furthermore, an image coding and decoding apparatus according to anembodiment of the present disclosure includes the image coding apparatusand the image decoding apparatus.

Each of the embodiments described below shows a general or specificexample. The numerical values, shapes, materials, structural elements,the arrangement and connection of the structural elements, steps, theorder of the steps etc. shown in the following embodiments are mereexamples, and therefore do not limit the scope of the Claims. Therefore,among the structural elements in the following embodiments, structuralelements not recited in any one of the independent claims showing themost generic concepts are described as arbitrary structural elements.

Embodiment 1

In an image coding method and an image decoding method according toEmbodiment 1, an indicator is added which clearly specifies CABACinitialization.

FIG. 12 is a diagram showing syntax of a slice header according toEmbodiment 1. A slice header 380 includes a new row 381 having a newsyntax element “entropy_default_initialization_flag.”

This entropy_default_initialization_flag is an indicator indicating,when set to a predetermined value, that CABAC of a slice is initializedwith a CABAC default (predetermined) value. The flag is a one-bitindicator having the first value such as “1” indicating that a slice isinitialized with a CABAC value and the second value such as “0”indicating that the initialization is performed by a different method.It is to be noted that the assignments of the values of “1” and “0” maybe switched.

The “different method” for determining initialization may be apredetermined method such as initialization based on a value of apreceding slice. However, the “different method” may include anotherdetermination flow similar to the flow shown in FIG. 9, thereby possiblyderiving an initialization method using a default CABAC value.

An image decoding apparatus according to this embodiment decodes abitstream of a coded video sequence including image slices at leastpartially coded by arithmetic coding. The image decoding apparatusincludes: a parsing unit which extracts, from bitstream data of a slice,an initialization indicator indicating whether or not an arithmeticdecoding probability model of the slice is initialized with apredetermined value; a control unit which controls whether or not thearithmetic decoding probability model is initialized with thepredetermined value, according to the initialization indicator; and anarithmetic decoding unit which decodes the slice by applying arithmeticdecoding.

For instance, the arithmetic coding may be context adaptive arithmeticcoding as defined in HEVC. However, the present disclosure is notlimited thereto.

The predetermined value is a default value known to an image codingapparatus and the image decoding apparatus, and does not change withcoded content.

The initialization indicator preferably refers to a 1-bit flag with “1”indicating that an arithmetic decoding probability model is initializedwith the predetermined value and “0” indicating that an arithmeticdecoding probability model is initialized by a different method.

Only when a target slice is a dependent slice, does the indicator needto be present. This is because when the target slice is a normal slice,the CABAC default value is used for initialization (refer to the case ofNo in S101 in FIG. 9). Thus, it is first analyzed whether or not thetarget slice is a dependent slice by checking a conditiondependent_slice_flag==1.

Moreover, when parallel processing of a slice and another slice isperformed, the initialization indicator (flag) is advantageous. Forexample, the parallel processing may be the WPP. Thus, only when acondition entropy coding_sync_enabled_flag==1 is true, does the syntaxof the slice header shown in FIG. 12 include an initialization indicatorentropy_default_initialization_flag.

Furthermore, the initialization indicator is appropriate only when theslice starts at the beginning of an LCU row. This is because immediateinitialization of CABAC is only then required to allow the parallelprocessing. This is indicated by a condition slice_address %PicWidthInCtbsY==0 in the syntax shown in FIG. 12.

As stated above, a syntax element “slice_address” indicates a start ofthe slice with an offset included in the bitstream. “PicWidthInCtbsY”indicates a width of a frame with the number of units of coding treeblocks (LCUs).

As shown in the row 381, a logical product of the three conditions isused for determination. In other words,entropy_default_initialization_flag is transmitted to clearly signal theinitialization method only when Expression 2 below is true.dependent slice flag==1&& entropy_coding_sync_enabled_flag==1&slice_address % PicWidthInCtibsY==0  (Expression 2)

When Expression 2 is not true, the initialization is performed based ona normal method, that is, WPP rules.

To put it another way, the image coding method and the image decodingmethod according to this embodiment include: subdividing a slice of animage into coding units corresponding to pixel blocks of the image; andextracting, by the parsing unit, an initialization indicator of headerdata, only when the slice is a dependent slice. An arithmetic decodingunit of dependent slices is initialized based on a context of anarithmetic decoding unit of parent slices corresponding to therespective dependent slices.

Moreover, only when parallel decoding of a row composed of the codingunits is allowed, may the parsing unit extract the initializationindicator of the header data.

Stated differently, according to this embodiment, the slice of the imageis subdivided into the coding units corresponding to the pixel blocks ofthe image, and the initialization indicator of the header data isextracted by the parsing unit only when the slice starts from thebeginning of the row composed of the coding unit blocks of the image.

FIG. 13 is a flow chart for a CABAC initialization determination methodfor a slice according to this embodiment. FIG. 13 assumes a case of thepicture 350 shown in FIG. 8. Assuming that the slice (4) (slice 354) andthe slice (1) (slice 351) are parsed in parallel, the followingdetermination is made.

First, it is determined whether or not the slice (4) is a dependentslice (S111). When the slice (4) is a dependent slice and otherconditions (parallel processing of rows is performed and a slice startsat the beginning of an LCU row) are satisfied (Yes in S111), aninitialization indicator “entropy_default_initialization_flag” ischecked to determine an initialization execution method (S112).

When the entropy_default_initialization_flag indicates application ofdefault initialization (No in S112), the default initialization isapplied (S114). In contrast, when theentropy_default_initialization_flag does not indicate the application ofthe default initialization (Yes in S112), initialization of the WPP isapplied in which a preceding slice is referred to (S113).

It is to be noted that this embodiment is not limited to signaling theinitialization indicator in the slice header. The same indicator may beembedded in another data structure, e.g. a supplemental enhancementinformation message.

Embodiment 2

Embodiment 1 makes it possible to achieve efficient parallel LCU rowprocessing such as the WPP and the dependent slice. On the other hand, anew syntax element is embedded in a slice header. In response,independence of CABAC initialization for slices during parallelprocessing may be achieved by modifying initialization rules, to avoidaddition of the new syntax element.

In Embodiment 2, the definition of the dependent slice and operationsfor dependent slice by an image coding apparatus and an image decodingapparatus are modified. This can be achieved by adding restrictions tobitstream standards.

In other words, the image decoding apparatus according to thisembodiment decodes a bitstream of a coded video sequence including imageslices subdivided into coding units and at least partially coded byarithmetic coding. The image decoding apparatus includes a parsing unitwhich extracts, from a bitstream, a first row of coding units and asecond row of coding units, wherein the coding units of the first rowand the second row are assigned to slices to avoid referring topartition information of a first slice in the first row when anarithmetic decoding unit for a second slice in the second row isinitialized. A start position of the first slice in the first row isbehind the second slice in the second row by a predetermined number ofcoding units. The image decoding apparatus further includes thearithmetic decoding unit which performs arithmetic decoding of the firstslice and the second slice at least partially in parallel, to decodeeach of the slices.

FIG. 14 is a diagram for describing the function of this embodiment, andshows a picture 390 partitioned into slices. The picture 390 includesfour slices that are a normal slice 391, a normal slice 392, a dependentslice 393, and a normal slice 394.

The three slices 391, 392, and 393 are included in the first row ofcoding units (LCUs). The slice 394 includes the whole second and thirdrows.

The first exemplary restriction applied to slicing and parallelprocessing on a row basis is that “when entropy_code_sync_enabled_flagand dependent_slice_enabled_flag are equal to 1, a normal slice maystart only at the beginning of a row of coding tree blocks.” Inaddition, the both flags, the entropy_code_sync_enabled_flag and thedependent_slice_enabled_flag, are included in a picture parameter set.It is to be noted that a coding tree block (CTB) and a largest codingunit (LCU) refer to the same unit. The CTB is used in a standard text(refer to NPL 3). In addition, although the LCU is used in a standardtext of the previous version, the CTB is used in a standard text of thecurrent version.

When the normal slice starts only at the beginning of a row of codingunits (LCU row), a dependent slice in another row which is subsequent tothe normal slice may always refer to CABAC states of the normal slice.Here, the CABAC states are CABAC states after the first LCU or the firsttwo LCUs are processed by the WPP. In addition, since a header of thedependent slice depends on a header of the normal slice preceding thedependent slice, when the normal slice 394 is lost, it is necessary todiscard the dependent slice.

Thus, in the first exemplary restriction, a normal slice always startsat the beginning of an LCU row. To put it differently, in an LCU row,the first slice is a normal slice, and the other slices are dependentslices. This means that the normal slice is allowed only as the firstslice in an LCU. In addition, in an LCU row, the slices other than thefirst slice are always dependent slices.

The first exemplary restriction does not need to be strict. It is onlynecessary to make at least one or two LCUs of the normal slice in apreceding row available to the dependent slice, to allow application ofWPP initialization.

Alternatively, the second exemplary restriction may be applied asanother restriction (rule). In the second exemplary restriction, anormal slice does not start after the coding tree block located secondin a row of coding tree blocks. The normal slice has to start at thebeginning of an LCU row, and thus, for example, it is not acceptable toset, as the normal slice, the slice 392 located second as shown in FIG.14.

It is sufficient that the start position of the first slice is beforethe coding unit located second in the first row. Moreover, the firstslice may be a normal slice, and the second slice may be a dependentslice using a slice header of the normal slice. Furthermore, the startposition of the first slice may be the beginning of the first row.

FIG. 15 is a flow chart for a determination process in a CABACinitialization method when the above rules are set. The followingdescribes the determination process using the example shown in FIG. 8.

First, it is determined whether or not the slice (4) is a dependentslice (S111). When the slice (4) is a dependent slice (Yes in S111), WWPinitialization is performed (S113). In contrast, when the slice (4) isnot a dependent slice (No in S111), default initialization is performed(S114).

As described above, a context adaptive entropy coding unit is used in animage coding method according to this embodiment. The image codingmethod is applied to a picture frame partitioned into at least twoportions. The at least two portions are a first portion and a secondportion which can be at least partially coded and decoded in parallel.

According to this embodiment, initialization of a context table of thesecond portion of a stream is determined, when the first portion of asubstream is subdivided into slices, by a method that does not depend onthe subdivision of the first portion. For instance, the WPP is performedfor each row (each LCU row), and thus a portion of the stream maycorrespond to the LCU row.

It is to be noted that the present disclosure is not limited to theabove exemplary restrictions. The exemplary restrictions may beformulated in a different manner. The following describes otherexemplary restrictions.

When a normal slice satisfies a condition of Expression 3 below, a slicestarting at the beginning of a subsequent LCU row is not a dependentslice.slice_address % PicWidthInCtbsY>1  (Expression 3)

For the sake of simplicity, the condition may be represented byExpression 4 below.slice_address % PicWidthInCtbsY !=0  (Expression 4)

Here, “!=” indicates inequality. When entropy_coding_sync_enabled_flagis equal to 1, that is, parallel processing of LCU rows is allowed,these restrictions are applicable. Moreover, “slice_address” indicates aposition of a slice starting in a bitstream, and the parameter“PicWidthInCtbsY” indicates a width of a picture (frame) in an LCU(coding tree block).

To put it another way, when the normal slice does not start at thebeginning of the row, a slice starting in an immediately subsequent rowis not a dependent slice (third exemplary restriction). This conditioneliminates the need for decoding of a slice in the second row to waituntil a normal slice at a position in the first row is parsed (decoded).

This means that when a normal slice starts at a position other than thebeginning of the first row, the second row immediately following thefirst row does not start with a dependent slice. Stated differently,when at least one of the slice located second and a subsequent slice inthe first row is a normal slice, the slice at the beginning of thesecond row is a normal slice.

The following describes the influence of the third exemplary restrictionwith reference to FIG. 16. A picture 400 shown in FIG. 16 includes threeslices 401 to 403 included in the first row. Among the three slices, thefirst two slices 401 and 402 located first and second are normal slices,and the slice 403 located third is a dependent slice.

This condition does not allow the slice 404 located fourth to be set asthe dependent slice. This is indicated in FIG. 16 by marking a cross tothe slice 404.

Thus, the bitstream may include normal slices and dependent slices, anddecoding of the normal slices and the dependent slices is based onparameters signaled in slice headers of the normal slices. When a normalslice starts at a position after the beginning of an LCU row, the nextLCU row does not start with a dependent slice.

Furthermore, specific examples are described with reference to FIG. 17Ato FIG. 17D. For example, as shown in FIG. 17A, when the first rowincludes a normal slice (3), the dependent slice cannot be set as aslice (4) at the beginning of the second row. In addition, when at leastone of a slice (2) and the slice (3) is a normal slice, the slice (4)cannot be set as the dependent slice. As a result, as shown in FIG. 17B,the slice (4) needs to be set as the normal slice. Furthermore, in thethird exemplary restriction, pictures as shown in FIG. 17C and FIG. 17Dare also allowed.

It is to be noted that although the pictures shown in FIG. 17A, FIG.17B, and FIG. 17D are not allowed in the above-stated first exemplaryrestriction, the picture shown in FIG. 17C is allowed. In addition,although the pictures shown in FIG. 17A and FIG. 17B are not allowed inthe second exemplary restriction, the pictures shown in FIG. 17C andFIG. 17D are allowed.

The following describes the fourth exemplary restriction with referenceto FIG. 18. When entropy_coding_sync_enabled_flag anddependent_slice_enabled_flag are equal to 1, no normal slice is allowedexcept the first slice in a frame (fourth exemplary restriction).

Stated differently, when parallel processing is allowed and dependentslices are enabled, a normal slice is allowed only as the first slice inthe frame. In short, all the slices in the frame are dependent slicesexcept the first slice. In other words, the slice at the beginning of animage is a normal slice, and all the other slices in the image aredependent slices.

A picture 410 shown in FIG. 18 includes five slices 411 to 415. Theslices 411, 412, and 415 are normal slices, and the slices 413 and 414are dependent slices. The normal slices 412 and 415 are not allowedexcept the normal slice 411 located first, according to the fourthexemplary restriction. In short, the slices 412 and 415 have to bedependent slices. Furthermore, among the pictures shown in FIG. 17A toFIG. 17D, only the picture shown in FIG. 17D is allowed in the fourthexemplary restriction.

It is to be noted that the usage of the fourth exemplary restrictioncauses a demerit regarding robustness against packet loss. The normalslices are usually used to reduce a dependency or error propagation in alossy environment. A frame where only the slice located first is anormal slice assumes a risk that all slices cannot be decoded when theslice located first cannot be decoded.

Moreover, the following restriction may be used as another restriction.When a slice (normal or dependent slice) starts in the middle of an LCUrow (i.e., a position different from the beginning of the row), the nextrow of coding units does not start with a dependent slice (fifthexemplary restriction).

It is to be noted that as is clear to a person skilled in the art, it ispossible to arbitrarily combine the restrictions described above. Inother words, the first to fifth exemplary restrictions may be applied incombination.

The following further describes another exemplary restriction. Whenentropy_coding_sync_enabled_flag is equal to 1, one LCU row cannot besubdivided into slices (sixth exemplary restriction). When thisrestriction is applied, the slices 412 and 413 are not allowed in theslice structure shown in FIG. 18. To put it another way, when parallelprocessing of rows of coding units is enabled, a slice is allowed onlyto include one entire row of coding units or entire rows of codingunits.

As stated above, the bitstream includes the normal slices and thedependent slices. The decoding of the normal slices and the dependentslices is based on the parameters signaled in the slice headers of thenormal slices. After it is determined that only the slice located firstin an image would be a normal slice and remaining slices would bedependent slices, the image is partitioned into slices.

Each of the slices includes the entirety of an m number of rows ofcoding units. Here, m is an integer greater than or equal to 1.Specifically, each of the slices includes the entirety of one or morerows.

When the dependent slices are enabled and one of the WPP and tile isenabled in addition to or instead of the application of the restriction,an indicator indicating the restriction may be embedded in thebitstream. For instance, this indicator is embedded in an SPS or a PPS.It is to be noted that the indicator may be embedded in another messagesuch as an SEI message or in any video usability information (VUI)message.

The image decoding apparatus identifies a restriction to be applied,based on the indicator. For example, this restriction is that a normalslice is allowed only at the beginning of an LCU row (WPP) or a tile. Itis to be noted that this is merely an exemplary restriction, and any ofthe above-mentioned restrictions, a combination of the restrictions, oran additional restriction not explicitly described may be applied.

For instance, the indicator may be a 1-bit flag indicating, for apredetermined restriction, whether or not the restriction is to beapplied. Selectable restrictions may be available, and informationindicating a selected restriction is signaled in the bitstream to theimage decoding apparatus. Stated differently, instead of explicitlylimiting the usage as described in the above examples, the image codingapparatus may notify the image decoding apparatus that such restrictionsare used. Thus, any of the examples regarding the restrictions can beapplied.

Thus, an image decoding method according to an implementation of thepresent disclosure includes obtaining, from a bitstream, a restrictionindicator indicating that partitioning of a picture is restricted, whenthe dependent slice is enabled. An image coding method according to animplementation of the present disclosure includes embedding, into abitstream, a restriction indicator indicating that partitioning of apicture is restricted, when the dependent slice is enabled.

It is to be noted that whether or not to add the indicator does not needto be determined depending on whether or not the WPP, tile, or dependentslice is enabled.

Furthermore, an image decoding method according to an implementation ofthe present disclosure is an image decoding method for decoding abitstream including a coded signal resulting from coding a plurality ofslices into which an image is partitioned and each of which includes aplurality of coding units (LCUs), and the image decoding method includesdecoding the coded signal. An image coding method according to animplementation of the present disclosure is an image coding method forcoding a plurality of slices into which an image is partitioned and eachof which includes a plurality of coding units (LCU), to generate abitstream, and the image coding method includes: partitioning the imageinto the slices; and coding the slices resulting from the partitioning.

Each of the slices is either a normal slice or a dependent slice. Thenormal slice is a slice having, in a slice header, information likely tobe used for another slice. The dependent slice is a slice which isdecoded using information included in a slice header of another slice.Here, the other slice is, for instance, a normal slice preceding andbeing closest to the dependent slice.

In the decoding, arithmetic decoding of a dependent slice is initializedusing a context of a parent slice whose slice header is used for thedependent slice. In the coding, arithmetic coding of a dependent sliceis initialized using a context of a parent slice whose slice header isused for the dependent slice.

The image includes a plurality of rows each of which includes aplurality of coding units.

In the partitioning, the image is partitioned into the tiles and theslices to satisfy one or more of the above-mentioned restrictions.

It may be that in the decoding, the first row and the second row aredecoded in parallel, and when the decoding of the second row is started,the second row is decoded without referring to partition informationindicating a slice structure of the first row. It may be that in thepartitioning, in the case where an image decoding apparatus decodes thefirst row and the second row in parallel, the image is partitioned intothe slices to allow the decoding of the second row without referring topartition information indicating a slice structure of the first row,when the image decoding apparatus starts decoding the second row.

Here, the partition information is, for example, information indicatinga slice position (start position) or a position of a slice header. Theimage decoding apparatus performs processing to determine theabove-stated CABAC initialization method by referring to this partitioninformation.

Furthermore, the parallel processing is the above-stated WPP, forexample. Specifically, in the decoding, arithmetic decoding of thesecond row is initialized using a context obtained after arithmeticdecoding of the coding unit located second in the first row. In thecoding, arithmetic coding of the second row is initialized using acontext obtained after arithmetic coding of the coding unit locatedsecond in the first row.

As stated above, the slice header has the information(dependent_slice_flag) indicating whether the slice is a normal slice ora dependent slice. In other words, the image decoding method includesobtaining, from a slice header, information indicating whether a sliceis a normal slice or a dependent slice. In addition, the image codingmethod includes embedding, into a slice header, information indicatingwhether a slice is a normal slice or a dependent slice.

As described above, this embodiment makes it possible to prevent thedependent slice processing from being delayed by at least two or atleast three coding units, by the CABAC initialization in view of thepreceding slices in the parallel processing. With this, the parallelprocessing of coding, decoding, and parsing of the rows can beefficiently performed.

It is to be noted that the present disclosure is not limited to theembodiment in which the slicing method is restricted. In addition, therestriction may relate to a slice from which a CABAC context can beobtained.

Embodiment 3

In this embodiment, a CABAC initialization method for a dependent sliceat a time of WPP is changed. Specifically, the parent slice assignmentrule for the dependent slice is changed.

For instance, a rule is determined in which a dependent slice alwaysobtains a slice header and a CABAC context from the same sliceregardless of subdivision of an LCU row into slices (and/or a type of asubsequent slice).

A picture 420 shown in FIG. 19 includes slices 421 to 424. In thecurrent HEVC, the slice 422 is a parent slice of the dependent slice424. In other words, a slice header of the dependent slice 424 isobtained from the slice 422, the closest preceding normal slice.

As described with reference to FIG. 9, there is a case where CABACinitialization is performed on the dependent slice using a normal slicewhich is at the beginning of a preceding LCU row. However, when theslice 422 is lost, although the CABAC initialization can be performed onthe slice 424, the slice 424 cannot be decoded due to the absence ofslice header information.

In view of this, in this embodiment, the dependent slice has, as theparent slice, the closest normal slice starting from the same row as thedependent slice or a row preceding the row of the dependent slice. Inthis embodiment, as shown in FIG. 19, the parent slice of the slice 424is set as the slice 421 according to this rule. The CABAC initializationis performed on the dependent slice 424 using a slice header of theslice 421 as well as CABAC states of the slice 421.

In addition, an arithmetic decoding unit of each dependent slice sets aslice dependency to perform initialization based on a context of anarithmetic decoding unit of the parent slice.

It is to be noted that information indicating a CABAC context table usedfor slice initialization may be explicitly signaled in an SEI message.In short, all initialization values considered to be used for CABACengine initialization may be explicitly signaled in the SEI message.

It is to be noted that the term “slice (normal slice or dependentslice)” used in the above description is sometimes referred to as a“slice segment (normal slice segment or dependent slice segment).”

In this case, a unit including one or more consecutive slice segments isreferred to as a “slice.” Specifically, one slice includes one normalslice segment and one or more consecutive dependent slice segmentsfollowing the normal slice segment. Stated differently, when a normalslice segment immediately follows another normal slice segment, a sliceincludes only the normal slice segment. In addition, when one or moredependent slice segments immediately follow a normal slice segment, aslice includes the normal slice segment and the one or more dependentslice segments. In a word, one slice ranges from a normal slice segmentto one or more dependent slices immediately preceding the next normalslice segment.

When such a definition is used, it can be said that the above-describedthird exemplary restrictions for the LCU rows and slices correspond tothe following definitions.

When entropy_coding_sync_enabled_flag is equal to 1 and the first codingtree block (LCU) in a slice is not the first coding tree block of a rowof coding tree blocks, it is a requirement of bitstream conformance thatthe last coding tree block in the slice shall belong to the same row ofcoding tree blocks as the first coding tree block in the slice.

Here, the case where the first coding tree block included in a slice isnot the first coding tree block in a coding tree block row is a casewhere a normal slice segment starts at a position other than thebeginning of the coding tree block row. The situation that the lastcoding tree block included in the slice belongs to the same coding treeblock row as the first coding tree block included in the slicecorresponds to the situation that the next row does not starts with adependent slice.

For example, in the example shown in FIG. 17B, slice segments (1) and(2) (denoted by slice (1) and slice (2) in FIG. 17B; such denotationswill likewise apply to the following slice segments) form one slice, aslice segment (3) forms one slice, and slice segments (4) and (5) formone slice. Among these slices, a slice the first coding tree block ofwhich is different from the first coding tree block in a coding treeblock row is only the slice formed of the slice segment (3). The lastcoding tree block in this slice belongs to the same coding tree blockrow (the first row) as the first coding tree block in the slice.Therefore, the structure shown in FIG. 17B is allowed.

On the other hand, in the example shown in FIG. 17A, slice segments (3)to (5) form one slice. The first coding tree block in this slice (thefirst coding tree block in the slice segment (3)) and the last codingtree block in this slice (the last coding tree block in the slicesegment (5)) belong to different coding tree block rows. Therefore, thestructure shown in FIG. 17A is not allowed.

In FIG. 17C, slice segments (1) to (3) form one slice, and slicesegments (4) and (5) form one slice. In FIG. 17D, slice segments (1) to(5) form one slice. This means that the slice the first coding treeblock of which is different from the first coding tree block in a codingtree block row, that is, the slice which starts in the middle of a row,is not present in FIG. 17C and FIG. 17D. Therefore, the structures shownin FIG. 17C and FIG. 17D are allowed.

When entropy_coding_sync_enabled_flag is equal to 1 and the first codingtree block (LCU) in a slice segment is not the first coding tree blockof a row of coding tree blocks, it is a requirement of bitstreamconformance that the last coding tree block in the slice segment shallbelong to the same row of coding tree blocks as the first coding treeblock in the slice segment.

Although the image coding method and the image decoding method accordingto the embodiments have been described thus far, the present disclosureis not limited to the embodiments.

The image coding method and the image decoding method are performed bythe image coding apparatus and the image decoding apparatus,respectively. The image coding apparatus and the image decodingapparatus have the same structures as, for instance, those shown in FIG.1 and FIG. 2, respectively, and characteristics steps included in theimage coding method and the image decoding method are executed by any ofthe respective processing units shown in FIG. 1 and FIG. 2 or processingunits not shown.

Moreover, the respective processing units included in the image codingapparatus and the image decoding apparatus according to the embodimentsare typically implemented as an LSI which is an integrated circuit.These processing units may be individually configured as single chips ormay be configured so that a part or all of the processing units areincluded in a single chip.

Furthermore, the method of circuit integration is not limited to LSIs,and implementation through a dedicated circuit or a genera-purposeprocessor is also possible. A Field Programmable Gate Array (FPGA) whichallows programming after LSI manufacturing or a reconfigurable processorwhich allows reconfiguration of the connections and settings of thecircuit cells inside the LSI may also be used.

Each of the structural elements in each of the above-describedembodiments may be configured in the form of dedicated hardware, or maybe implemented by executing a software program suited to the structuralelement. Each of the structural elements may be implemented by means ofa program execution unit, such as a CPU or a processor, reading andexecuting the software program recorded on a recording medium such as ahard disk or semiconductor memory.

In other words, each of the image coding apparatus and the imagedecoding apparatus includes control circuitry and storage electricallyconnected to the control circuitry (accessible from the controlcircuitry). The control circuitry includes at least one of the dedicatedhardware and the program execution unit. In addition, when the controlcircuitry includes the program execution unit, the storage stores asoftware program executed by the program execution unit.

Moreover, the present disclosure may be the software program, or anon-transitory computer-readable recording medium on which the programis recorded. Furthermore, it goes without saying that the program can bedistributed via a transmission medium such as the Internet.

Moreover, all numerical figures used in the forgoing description aremerely exemplified for describing the present disclosure in specificterms, and thus the present disclosure is not limited to the exemplifiednumerical figures.

Furthermore, the separation of the functional blocks in the blockdiagrams is merely an example, and plural functional blocks may beimplemented as a single functional block, a single functional block maybe separated into plural functional blocks, or part of functions of afunctional block may be transferred to another functional block. Inaddition, the functions of functional blocks having similar functionsmay be processed, in parallel or by time-sharing, by single hardware orsoftware.

Moreover, the sequence in which the steps included in the image codingmethod and the image decoding method are executed is given as an exampleto describe the present disclosure in specific terms, and thus othersequences are possible. Furthermore, part of the steps may be executedsimultaneously (in parallel) with another step.

Although the exemplary embodiments are described above, the Claims inthis application are not limited to these embodiments. Those skilled inthe art would readily appreciate that, without departing from theteachings and advantages of the subject matter recited in the appendedClaims, various modifications may be made in the above-describedembodiments and other embodiments may be obtained by arbitrarilycombining structural elements in the above-described embodiments.Therefore, such modification examples and other embodiments are alsoincluded in the present disclosure.

Embodiment 4

The processing described in each of embodiments can be simplyimplemented in an independent computer system, by recording, in arecording medium, a program for implementing the configurations of themoving picture coding method (image coding method) and the movingpicture decoding method (image decoding method) described in each ofembodiments. The recording media may be any recording media as long asthe program can be recorded, such as a magnetic disk, an optical disk, amagnetic optical disk, an IC card, and a semiconductor memory.

Hereinafter, the applications to the moving picture coding method (imagecoding method) and the moving picture decoding method (image decodingmethod) described in each of embodiments and systems using thereof willbe described. The system has a feature of having an image coding anddecoding apparatus that includes an image coding apparatus using theimage coding method and an image decoding apparatus using the imagedecoding method. Other configurations in the system can be changed asappropriate depending on the cases.

FIG. 20 illustrates an overall configuration of a content providingsystem ex100 for implementing content distribution services. The areafor providing communication services is divided into cells of desiredsize, and base stations ex106, ex107, ex108, ex109, and ex110 which arefixed wireless stations are placed in each of the cells.

The content providing system ex100 is connected to devices, such as acomputer ex111, a personal digital assistant (PDA) ex112, a cameraex113, a cellular phone ex114 and a game machine ex115, via the Internetex101, an Internet service provider ex102, a telephone network ex104, aswell as the base stations ex106 to ex110, respectively.

However, the configuration of the content providing system ex100 is notlimited to the configuration shown in FIG. 20, and a combination inwhich any of the elements are connected is acceptable. In addition, eachdevice may be directly connected to the telephone network ex104, ratherthan via the base stations ex106 to ex110 which are the fixed wirelessstations. Furthermore, the devices may be interconnected to each othervia a short distance wireless communication and others.

The camera ex113, such as a digital video camera, is capable ofcapturing video. A camera ex116, such as a digital camera, is capable ofcapturing both still images and video. Furthermore, the cellular phoneex114 may be the one that meets any of the standards such as GlobalSystem for Mobile Communications (GSM) (registered trademark), CodeDivision Multiple Access (CDMA), Wideband-Code Division Multiple Access(W-CDMA), Long Term Evolution (LTE), and High Speed Packet Access(HSPA). Alternatively, the cellular phone ex114 may be a PersonalHandyphone System (PHS).

In the content providing system ex100, a streaming server ex103 isconnected to the camera ex113 and others via the telephone network ex104and the base station ex109, which enables distribution of images of alive show and others. In such a distribution, a content (for example,video of a music live show) captured by the user using the camera ex113is coded as described above in each of embodiments (i.e., the camerafunctions as the image coding apparatus according to an aspect of thepresent disclosure), and the coded content is transmitted to thestreaming server ex103. On the other hand, the streaming server ex103carries out stream distribution of the transmitted content data to theclients upon their requests. The clients include the computer ex111, thePDA ex112, the camera ex113, the cellular phone ex114, and the gamemachine ex115 that are capable of decoding the above-mentioned codeddata. Each of the devices that have received the distributed datadecodes and reproduces the coded data (i.e., functions as the imagedecoding apparatus according to an aspect of the present disclosure).

The captured data may be coded by the camera ex113 or the streamingserver ex103 that transmits the data, or the coding processes may beshared between the camera ex113 and the streaming server ex103.Similarly, the distributed data may be decoded by the clients or thestreaming server ex103, or the decoding processes may be shared betweenthe clients and the streaming server ex103. Furthermore, the data of thestill images and video captured by not only the camera ex113 but alsothe camera ex116 may be transmitted to the streaming server ex103through the computer ex111. The coding processes may be performed by thecamera ex116, the computer ex111, or the streaming server ex103, orshared among them.

Furthermore, the coding and decoding processes may be performed by anLSI ex500 generally included in each of the computer ex111 and thedevices. The LSI ex500 may be configured of a single chip or a pluralityof chips. Software for coding and decoding video may be integrated intosome type of a recording medium (such as a CD-ROM, a flexible disk, anda hard disk) that is readable by the computer ex111 and others, and thecoding and decoding processes may be performed using the software.Furthermore, when the cellular phone ex114 is equipped with a camera,the video data obtained by the camera may be transmitted. The video datais data coded by the LSI ex500 included in the cellular phone ex114.

Furthermore, the streaming server ex103 may be composed of servers andcomputers, and may decentralize data and process the decentralized data,record, or distribute data.

As described above, the clients may receive and reproduce the coded datain the content providing system ex100. In other words, the clients canreceive and decode information transmitted by the user, and reproducethe decoded data in real time in the content providing system ex100, sothat the user who does not have any particular right and equipment canimplement personal broadcasting.

Aside from the example of the content providing system ex100, at leastone of the moving picture coding apparatus (image coding apparatus) andthe moving picture decoding apparatus (image decoding apparatus)described in each of embodiments may be implemented in a digitalbroadcasting system ex200 illustrated in FIG. 21. More specifically, abroadcast station ex201 communicates or transmits, via radio waves to abroadcast satellite ex202, multiplexed data obtained by multiplexingaudio data and others onto video data. The video data is data coded bythe moving picture coding method described in each of embodiments (i.e.,data coded by the image coding apparatus according to an aspect of thepresent disclosure). Upon receipt of the multiplexed data, the broadcastsatellite ex202 transmits radio waves for broadcasting. Then, a home-useantenna ex204 with a satellite broadcast reception function receives theradio waves. Next, a device such as a television (receiver) ex300 and aset top box (STB) ex217 decodes the received multiplexed data, andreproduces the decoded data (i.e., functions as the image decodingapparatus according to an aspect of the present disclosure).

Furthermore, a reader/recorder ex218 (i) reads and decodes themultiplexed data recorded on a recording medium ex215, such as a DVD anda BD, or (i) codes video signals in the recording medium ex215, and insome cases, writes data obtained by multiplexing an audio signal on thecoded data. The reader/recorder ex218 can include the moving picturedecoding apparatus or the moving picture coding apparatus as shown ineach of embodiments. In this case, the reproduced video signals aredisplayed on the monitor ex219, and can be reproduced by another deviceor system using the recording medium ex215 on which the multiplexed datais recorded. It is also possible to implement the moving picturedecoding apparatus in the set top box ex217 connected to the cable ex203for a cable television or to the antenna ex204 for satellite and/orterrestrial broadcasting, so as to display the video signals on themonitor ex219 of the television ex300. The moving picture decodingapparatus may be implemented not in the set top box but in thetelevision ex300.

FIG. 22 illustrates the television (receiver) ex300 that uses the movingpicture coding method and the moving picture decoding method describedin each of embodiments. The television ex300 includes: a tuner ex301that obtains or provides multiplexed data obtained by multiplexing audiodata onto video data, through the antenna ex204 or the cable ex203, etc.that receives a broadcast; a modulation/demodulation unit ex302 thatdemodulates the received multiplexed data or modulates data intomultiplexed data to be supplied outside; and amultiplexing/demultiplexing unit ex303 that demultiplexes the modulatedmultiplexed data into video data and audio data, or multiplexes videodata and audio data coded by a signal processing unit ex306 into data.

The television ex300 further includes: a signal processing unit ex306including an audio signal processing unit ex304 and a video signalprocessing unit ex305 that decode audio data and video data and codeaudio data and video data, respectively (which function as the imagecoding apparatus and the image decoding apparatus according to theaspects of the present disclosure); and an output unit ex309 including aspeaker ex307 that provides the decoded audio signal, and a display unitex308 that displays the decoded video signal, such as a display.Furthermore, the television ex300 includes an interface unit ex317including an operation input unit ex312 that receives an input of a useroperation. Furthermore, the television ex300 includes a control unitex310 that controls overall each constituent element of the televisionex300, and a power supply circuit unit ex311 that supplies power to eachof the elements. Other than the operation input unit ex312, theinterface unit ex317 may include: a bridge ex313 that is connected to anexternal device, such as the reader/recorder ex218; a slot unit ex314for enabling attachment of the recording medium ex216, such as an SDcard; a driver ex315 to be connected to an external recording medium,such as a hard disk; and a modem ex316 to be connected to a telephonenetwork. Here, the recording medium ex216 can electrically recordinformation using a non-volatile/volatile semiconductor memory elementfor storage. The constituent elements of the television ex300 areconnected to each other through a synchronous bus.

First, the configuration in which the television ex300 decodesmultiplexed data obtained from outside through the antenna ex204 andothers and reproduces the decoded data will be described. In thetelevision ex300, upon a user operation through a remote controllerex220 and others, the multiplexing/demultiplexing unit ex303demultiplexes the multiplexed data demodulated by themodulation/demodulation unit ex302, under control of the control unitex310 including a CPU. Furthermore, the audio signal processing unitex304 decodes the demultiplexed audio data, and the video signalprocessing unit ex305 decodes the demultiplexed video data, using thedecoding method described in each of embodiments, in the televisionex300. The output unit ex309 provides the decoded video signal and audiosignal outside, respectively. When the output unit ex309 provides thevideo signal and the audio signal, the signals may be temporarily storedin buffers ex318 and ex319, and others so that the signals arereproduced in synchronization with each other. Furthermore, thetelevision ex300 may read multiplexed data not through a broadcast andothers but from the recording media ex215 and ex216, such as a magneticdisk, an optical disk, and a SD card. Next, a configuration in which thetelevision ex300 codes an audio signal and a video signal, and transmitsthe data outside or writes the data on a recording medium will bedescribed. In the television ex300, upon a user operation through theremote controller ex220 and others, the audio signal processing unitex304 codes an audio signal, and the video signal processing unit ex305codes a video signal, under control of the control unit ex310 using thecoding method described in each of embodiments. Themultiplexing/demultiplexing unit ex303 multiplexes the coded videosignal and audio signal, and provides the resulting signal outside. Whenthe multiplexing/demultiplexing unit ex303 multiplexes the video signaland the audio signal, the signals may be temporarily stored in thebuffers ex320 and ex321, and others so that the signals are reproducedin synchronization with each other. Here, the buffers ex318, ex319,ex320, and ex321 may be plural as illustrated, or at least one buffermay be shared in the television ex300. Furthermore, data may be storedin a buffer so that the system overflow and underflow may be avoidedbetween the modulation/demodulation unit ex302 and themultiplexing/demultiplexing unit ex303, for example.

Furthermore, the television ex300 may include a configuration forreceiving an AV input from a microphone or a camera other than theconfiguration for obtaining audio and video data from a broadcast or arecording medium, and may code the obtained data. Although thetelevision ex300 can code, multiplex, and provide outside data in thedescription, it may be capable of only receiving, decoding, andproviding outside data but not the coding, multiplexing, and providingoutside data.

Furthermore, when the reader/recorder ex218 reads or writes multiplexeddata from or on a recording medium, one of the television ex300 and thereader/recorder ex218 may decode or code the multiplexed data, and thetelevision ex300 and the reader/recorder ex218 may share the decoding orcoding.

As an example, FIG. 23 illustrates a configuration of an informationreproducing/recording unit ex400 when data is read or written from or onan optical disk. The information reproducing/recording unit ex400includes constituent elements ex401, ex402, ex403, ex404, ex405, ex406,and ex407 to be described hereinafter. The optical head ex401 irradiatesa laser spot in a recording surface of the recording medium ex215 thatis an optical disk to write information, and detects reflected lightfrom the recording surface of the recording medium ex215 to read theinformation. The modulation recording unit ex402 electrically drives asemiconductor laser included in the optical head ex401, and modulatesthe laser light according to recorded data. The reproductiondemodulating unit ex403 amplifies a reproduction signal obtained byelectrically detecting the reflected light from the recording surfaceusing a photo detector included in the optical head ex401, anddemodulates the reproduction signal by separating a signal componentrecorded on the recording medium ex215 to reproduce the necessaryinformation. The buffer ex404 temporarily holds the information to berecorded on the recording medium ex215 and the information reproducedfrom the recording medium ex215. The disk motor ex405 rotates therecording medium ex215. The servo control unit ex406 moves the opticalhead ex401 to a predetermined information track while controlling therotation drive of the disk motor ex405 so as to follow the laser spot.The system control unit ex407 controls overall the informationreproducing/recording unit ex400. The reading and writing processes canbe implemented by the system control unit ex407 using variousinformation stored in the buffer ex404 and generating and adding newinformation as necessary, and by the modulation recording unit ex402,the reproduction demodulating unit ex403, and the servo control unitex406 that record and reproduce information through the optical headex401 while being operated in a coordinated manner. The system controlunit ex407 includes, for example, a microprocessor, and executesprocessing by causing a computer to execute a program for read andwrite.

Although the optical head ex401 irradiates a laser spot in thedescription, it may perform high-density recording using near fieldlight.

FIG. 24 illustrates the recording medium ex215 that is the optical disk.On the recording surface of the recording medium ex215, guide groovesare spirally formed, and an information track ex230 records, in advance,address information indicating an absolute position on the diskaccording to change in a shape of the guide grooves. The addressinformation includes information for determining positions of recordingblocks ex231 that are a unit for recording data. Reproducing theinformation track ex230 and reading the address information in anapparatus that records and reproduces data can lead to determination ofthe positions of the recording blocks. Furthermore, the recording mediumex215 includes a data recording area ex233, an inner circumference areaex232, and an outer circumference area ex234. The data recording areaex233 is an area for use in recording the user data. The innercircumference area ex232 and the outer circumference area ex234 that areinside and outside of the data recording area ex233, respectively arefor specific use except for recording the user data. The informationreproducing/recording unit 400 reads and writes coded audio, coded videodata, or multiplexed data obtained by multiplexing the coded audio andvideo data, from and on the data recording area ex233 of the recordingmedium ex215.

Although an optical disk having a layer, such as a DVD and a BD isdescribed as an example in the description, the optical disk is notlimited to such, and may be an optical disk having a multilayerstructure and capable of being recorded on a part other than thesurface. Furthermore, the optical disk may have a structure formultidimensional recording/reproduction, such as recording ofinformation using light of colors with different wavelengths in the sameportion of the optical disk and for recording information havingdifferent layers from various angles.

Furthermore, a car ex210 having an antenna ex205 can receive data fromthe satellite ex202 and others, and reproduce video on a display devicesuch as a car navigation system ex211 set in the car ex210, in thedigital broadcasting system ex200. Here, a configuration of the carnavigation system ex211 will be a configuration, for example, includinga GPS receiving unit from the configuration illustrated in FIG. 22. Thesame will be true for the configuration of the computer ex111, thecellular phone ex114, and others.

FIG. 25A illustrates the cellular phone ex114 that uses the movingpicture coding method and the moving picture decoding method describedin embodiments. The cellular phone ex114 includes: an antenna ex350 fortransmitting and receiving radio waves through the base station ex110; acamera unit ex365 capable of capturing moving and still images; and adisplay unit ex358 such as a liquid crystal display for displaying thedata such as decoded video captured by the camera unit ex365 or receivedby the antenna ex350. The cellular phone ex114 further includes: a mainbody unit including an operation key unit ex366; an audio output unitex357 such as a speaker for output of audio; an audio input unit ex356such as a microphone for input of audio; a memory unit ex367 for storingcaptured video or still pictures, recorded audio, coded or decoded dataof the received video, the still pictures, e-mails, or others; and aslot unit ex364 that is an interface unit for a recording medium thatstores data in the same manner as the memory unit ex367.

Next, an example of a configuration of the cellular phone ex114 will bedescribed with reference to FIG. 25B. In the cellular phone ex114, amain control unit ex360 designed to control overall each unit of themain body including the display unit ex358 as well as the operation keyunit ex366 is connected mutually, via a synchronous bus ex370, to apower supply circuit unit ex361, an operation input control unit ex362,a video signal processing unit ex355, a camera interface unit ex363, aliquid crystal display (LCD) control unit ex359, amodulation/demodulation unit ex352, a multiplexing/demultiplexing unitex353, an audio signal processing unit ex354, the slot unit ex364, andthe memory unit ex367.

When a call-end key or a power key is turned ON by a user's operation,the power supply circuit unit ex361 supplies the respective units withpower from a battery pack so as to activate the cell phone ex114.

In the cellular phone ex114, the audio signal processing unit ex354converts the audio signals collected by the audio input unit ex356 invoice conversation mode into digital audio signals under the control ofthe main control unit ex360 including a CPU, ROM, and RAM. Then, themodulation/demodulation unit ex352 performs spread spectrum processingon the digital audio signals, and the transmitting and receiving unitex351 performs digital-to-analog conversion and frequency conversion onthe data, so as to transmit the resulting data via the antenna ex350.Also, in the cellular phone ex114, the transmitting and receiving unitex351 amplifies the data received by the antenna ex350 in voiceconversation mode and performs frequency conversion and theanalog-to-digital conversion on the data. Then, themodulation/demodulation unit ex352 performs inverse spread spectrumprocessing on the data, and the audio signal processing unit ex354converts it into analog audio signals, so as to output them via theaudio output unit ex357.

Furthermore, when an e-mail in data communication mode is transmitted,text data of the e-mail inputted by operating the operation key unitex366 and others of the main body is sent out to the main control unitex360 via the operation input control unit ex362. The main control unitex360 causes the modulation/demodulation unit ex352 to perform spreadspectrum processing on the text data, and the transmitting and receivingunit ex351 performs the digital-to-analog conversion and the frequencyconversion on the resulting data to transmit the data to the basestation ex110 via the antenna ex350. When an e-mail is received,processing that is approximately inverse to the processing fortransmitting an e-mail is performed on the received data, and theresulting data is provided to the display unit ex358.

When video, still images, or video and audio in data communication modeis or are transmitted, the video signal processing unit ex355 compressesand codes video signals supplied from the camera unit ex365 using themoving picture coding method shown in each of embodiments (i.e.,functions as the image coding apparatus according to the aspect of thepresent disclosure), and transmits the coded video data to themultiplexing/demultiplexing unit ex353. In contrast, during when thecamera unit ex365 captures video, still images, and others, the audiosignal processing unit ex354 codes audio signals collected by the audioinput unit ex356, and transmits the coded audio data to themultiplexing/demultiplexing unit ex353.

The multiplexing/demultiplexing unit ex353 multiplexes the coded videodata supplied from the video signal processing unit ex355 and the codedaudio data supplied from the audio signal processing unit ex354, using apredetermined method. Then, the modulation/demodulation unit(modulation/demodulation circuit unit) ex352 performs spread spectrumprocessing on the multiplexed data, and the transmitting and receivingunit ex351 performs digital-to-analog conversion and frequencyconversion on the data so as to transmit the resulting data via theantenna ex350.

When receiving data of a video file which is linked to a Web page andothers in data communication mode or when receiving an e-mail with videoand/or audio attached, in order to decode the multiplexed data receivedvia the antenna ex350, the multiplexing/demultiplexing unit ex353demultiplexes the multiplexed data into a video data bit stream and anaudio data bit stream, and supplies the video signal processing unitex355 with the coded video data and the audio signal processing unitex354 with the coded audio data, through the synchronous bus ex370. Thevideo signal processing unit ex355 decodes the video signal using amoving picture decoding method corresponding to the moving picturecoding method shown in each of embodiments (i.e., functions as the imagedecoding apparatus according to the aspect of the present disclosure),and then the display unit ex358 displays, for instance, the video andstill images included in the video file linked to the Web page via theLCD control unit ex359. Furthermore, the audio signal processing unitex354 decodes the audio signal, and the audio output unit ex357 providesthe audio.

Furthermore, similarly to the television ex300, a terminal such as thecellular phone ex114 probably has 3 types of implementationconfigurations including not only (i) a transmitting and receivingterminal including both a coding apparatus and a decoding apparatus, butalso (ii) a transmitting terminal including only a coding apparatus and(iii) a receiving terminal including only a decoding apparatus. Althoughthe digital broadcasting system ex200 receives and transmits themultiplexed data obtained by multiplexing audio data onto video data inthe description, the multiplexed data may be data obtained bymultiplexing not audio data but character data related to video ontovideo data, and may be not multiplexed data but video data itself.

As such, the moving picture coding method and the moving picturedecoding method in each of embodiments can be used in any of the devicesand systems described. Thus, the advantages described in each ofembodiments can be obtained.

Furthermore, various modifications and revisions can be made in any ofthe embodiments in the present disclosure.

Embodiment 5

Video data can be generated by switching, as necessary, between (i) themoving picture coding method or the moving picture coding apparatusshown in each of embodiments and (ii) a moving picture coding method ora moving picture coding apparatus in conformity with a differentstandard, such as MPEG-2, MPEG-4 AVC, and VC-1.

Here, when a plurality of video data that conforms to the differentstandards is generated and is then decoded, the decoding methods need tobe selected to conform to the different standards. However, since towhich standard each of the plurality of the video data to be decodedconform cannot be detected, an appropriate decoding method cannot beselected.

In view of this, multiplexed data obtained by multiplexing audio dataand others onto video data has a structure including identificationinformation indicating to which standard the video data conforms. Thespecific structure of the multiplexed data including the video datagenerated in the moving picture coding method and by the moving picturecoding apparatus shown in each of embodiments will be hereinafterdescribed. The multiplexed data is a digital stream in the MPEG-2Transport Stream format.

FIG. 26 illustrates a structure of the multiplexed data. As illustratedin FIG. 26, the multiplexed data can be obtained by multiplexing atleast one of a video stream, an audio stream, a presentation graphicsstream (PG), and an interactive graphics stream. The video streamrepresents primary video and secondary video of a movie, the audiostream (IG) represents a primary audio part and a secondary audio partto be mixed with the primary audio part, and the presentation graphicsstream represents subtitles of the movie. Here, the primary video isnormal video to be displayed on a screen, and the secondary video isvideo to be displayed on a smaller window in the primary video.Furthermore, the interactive graphics stream represents an interactivescreen to be generated by arranging the GUI components on a screen. Thevideo stream is coded in the moving picture coding method or by themoving picture coding apparatus shown in each of embodiments, or in amoving picture coding method or by a moving picture coding apparatus inconformity with a conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1. The audio stream is coded in accordance with a standard, such asDolby-AC-3, Dolby Digital Plus, MLP, DTS, DTS-HD, and linear PCM.

Each stream included in the multiplexed data is identified by PID. Forexample, 0x1011 is allocated to the video stream to be used for video ofa movie, 0x1100 to 0x111F are allocated to the audio streams, 0x1200 to0x121F are allocated to the presentation graphics streams, 0x1400 to0x141F are allocated to the interactive graphics streams, 0x1 B00 to 0x1B1F are allocated to the video streams to be used for secondary video ofthe movie, and 0x1A00 to 0x1A1F are allocated to the audio streams to beused for the secondary audio to be mixed with the primary audio.

FIG. 27 schematically illustrates how data is multiplexed. First, avideo stream ex235 composed of video frames and an audio stream ex238composed of audio frames are transformed into a stream of PES packetsex236 and a stream of PES packets ex239, and further into TS packetsex237 and TS packets ex240, respectively. Similarly, data of apresentation graphics stream ex241 and data of an interactive graphicsstream ex244 are transformed into a stream of PES packets ex242 and astream of PES packets ex245, and further into TS packets ex243 and TSpackets ex246, respectively. These TS packets are multiplexed into astream to obtain multiplexed data ex247.

FIG. 28 illustrates how a video stream is stored in a stream of PESpackets in more detail. The first bar in FIG. 28 shows a video framestream in a video stream. The second bar shows the stream of PESpackets. As indicated by arrows denoted as yy1, yy2, yy3, and yy4 inFIG. 28, the video stream is divided into pictures as I pictures, Bpictures, and P pictures each of which is a video presentation unit, andthe pictures are stored in a payload of each of the PES packets. Each ofthe PES packets has a PES header, and the PES header stores aPresentation Time-Stamp (PTS) indicating a display time of the picture,and a Decoding Time-Stamp (DTS) indicating a decoding time of thepicture.

FIG. 29 illustrates a format of TS packets to be finally written on themultiplexed data. Each of the TS packets is a 188-byte fixed lengthpacket including a 4-byte TS header having information, such as a PIDfor identifying a stream, and a 184-byte TS payload for storing data.The PES packets are divided, and stored in the TS payloads,respectively. When a BD ROM is used, each of the TS packets is given a4-byte TP_Extra_Header, thus resulting in 192-byte source packets. Thesource packets are written on the multiplexed data. The TP_Extra_Headerstores information such as an Arrival_Time_Stamp (ATS). The ATS shows atransfer start time at which each of the TS packets is to be transferredto a PID filter. The source packets are arranged in the multiplexed dataas shown at the bottom of FIG. 29. The numbers incrementing from thehead of the multiplexed data are called source packet numbers (SPNs).

Each of the TS packets included in the multiplexed data includes notonly streams of audio, video, subtitles and others, but also a ProgramAssociation Table (PAT), a Program Map Table (PMT), and a Program ClockReference (PCR). The PAT shows what a PID in a PMT used in themultiplexed data indicates, and a PID of the PAT itself is registered aszero. The PMT stores PIDs of the streams of video, audio, subtitles andothers included in the multiplexed data, and attribute information ofthe streams corresponding to the PIDs. The PMT also has variousdescriptors relating to the multiplexed data. The descriptors haveinformation such as copy control information showing whether copying ofthe multiplexed data is permitted or not. The PCR stores STC timeinformation corresponding to an ATS showing when the PCR packet istransferred to a decoder, in order to achieve synchronization between anArrival Time Clock (ATC) that is a time axis of ATSs, and an System TimeClock (STC) that is a time axis of PTSs and DTSs.

FIG. 30 illustrates the data structure of the PMT in detail. A PMTheader is disposed at the top of the PMT. The PMT header describes thelength of data included in the PMT and others. A plurality ofdescriptors relating to the multiplexed data is disposed after the PMTheader. Information such as the copy control information is described inthe descriptors. After the descriptors, a plurality of pieces of streaminformation relating to the streams included in the multiplexed data isdisposed. Each piece of stream information includes stream descriptorseach describing information, such as a stream type for identifying acompression codec of a stream, a stream PID, and stream attributeinformation (such as a frame rate or an aspect ratio). The streamdescriptors are equal in number to the number of streams in themultiplexed data.

When the multiplexed data is recorded on a recording medium and others,it is recorded together with multiplexed data information files.

Each of the multiplexed data information files is management informationof the multiplexed data as shown in FIG. 31. The multiplexed datainformation files are in one to one correspondence with the multiplexeddata, and each of the files includes multiplexed data information,stream attribute information, and an entry map.

As illustrated in FIG. 31, the multiplexed data information includes asystem rate, a reproduction start time, and a reproduction end time. Thesystem rate indicates the maximum transfer rate at which a system targetdecoder to be described later transfers the multiplexed data to a PIDfilter. The intervals of the ATSs included in the multiplexed data areset to not higher than a system rate. The reproduction start timeindicates a PTS in a video frame at the head of the multiplexed data. Aninterval of one frame is added to a PTS in a video frame at the end ofthe multiplexed data, and the PTS is set to the reproduction end time.

As shown in FIG. 32, a piece of attribute information is registered inthe stream attribute information, for each PID of each stream includedin the multiplexed data. Each piece of attribute information hasdifferent information depending on whether the corresponding stream is avideo stream, an audio stream, a presentation graphics stream, or aninteractive graphics stream. Each piece of video stream attributeinformation carries information including what kind of compression codecis used for compressing the video stream, and the resolution, aspectratio and frame rate of the pieces of picture data that is included inthe video stream. Each piece of audio stream attribute informationcarries information including what kind of compression codec is used forcompressing the audio stream, how many channels are included in theaudio stream, which language the audio stream supports, and how high thesampling frequency is. The video stream attribute information and theaudio stream attribute information are used for initialization of adecoder before the player plays back the information.

In the present embodiment, the multiplexed data to be used is of astream type included in the PMT. Furthermore, when the multiplexed datais recorded on a recording medium, the video stream attributeinformation included in the multiplexed data information is used. Morespecifically, the moving picture coding method or the moving picturecoding apparatus described in each of embodiments includes a step or aunit for allocating unique information indicating video data generatedby the moving picture coding method or the moving picture codingapparatus in each of embodiments, to the stream type included in the PMTor the video stream attribute information. With the configuration, thevideo data generated by the moving picture coding method or the movingpicture coding apparatus described in each of embodiments can bedistinguished from video data that conforms to another standard.

Furthermore, FIG. 33 illustrates steps of the moving picture decodingmethod according to the present embodiment. In Step exS100, the streamtype included in the PMT or the video stream attribute informationincluded in the multiplexed data information is obtained from themultiplexed data. Next, in Step exS101, it is determined whether or notthe stream type or the video stream attribute information indicates thatthe multiplexed data is generated by the moving picture coding method orthe moving picture coding apparatus in each of embodiments. When it isdetermined that the stream type or the video stream attributeinformation indicates that the multiplexed data is generated by themoving picture coding method or the moving picture coding apparatus ineach of embodiments, in Step exS102, decoding is performed by the movingpicture decoding method in each of embodiments. Furthermore, when thestream type or the video stream attribute information indicatesconformance to the conventional standards, such as MPEG-2, MPEG-4 AVC,and VC-1, in Step exS103, decoding is performed by a moving picturedecoding method in conformity with the conventional standards.

As such, allocating a new unique value to the stream type or the videostream attribute information enables determination whether or not themoving picture decoding method or the moving picture decoding apparatusthat is described in each of embodiments can perform decoding. Even whenmultiplexed data that conforms to a different standard is input, anappropriate decoding method or apparatus can be selected. Thus, itbecomes possible to decode information without any error. Furthermore,the moving picture coding method or apparatus, or the moving picturedecoding method or apparatus in the present embodiment can be used inthe devices and systems described above.

Embodiment 6

Each of the moving picture coding method, the moving picture codingapparatus, the moving picture decoding method, and the moving picturedecoding apparatus in each of embodiments is typically achieved in theform of an integrated circuit or a Large Scale Integrated (LSI) circuit.As an example of the LSI, FIG. 34 illustrates a configuration of the LSIex500 that is made into one chip. The LSI ex500 includes elements ex501,ex502, ex503, ex504, ex505, ex506, ex507, ex508, and ex509 to bedescribed below, and the elements are connected to each other through abus ex510. The power supply circuit unit ex505 is activated by supplyingeach of the elements with power when the power supply circuit unit ex505is turned on.

For example, when coding is performed, the LSI ex500 receives an AVsignal from a microphone ex117, a camera ex113, and others through an AVIO ex509 under control of a control unit ex501 including a CPU ex502, amemory controller ex503, a stream controller ex504, and a drivingfrequency control unit ex512. The received AV signal is temporarilystored in an external memory ex511, such as an SDRAM. Under control ofthe control unit ex501, the stored data is segmented into data portionsaccording to the processing amount and speed to be transmitted to asignal processing unit ex507. Then, the signal processing unit ex507codes an audio signal and/or a video signal. Here, the coding of thevideo signal is the coding described in each of embodiments.Furthermore, the signal processing unit ex507 sometimes multiplexes thecoded audio data and the coded video data, and a stream JO ex506provides the multiplexed data outside. The provided multiplexed data istransmitted to the base station ex107, or written on the recordingmedium ex215. When data sets are multiplexed, the data should betemporarily stored in the buffer ex508 so that the data sets aresynchronized with each other. Although the memory ex511 is an elementoutside the LSI ex500, it may be included in the LSI ex500. The bufferex508 is not limited to one buffer, but may be composed of buffers.Furthermore, the LSI ex500 may be made into one chip or a plurality ofchips. Furthermore, although the control unit ex501 includes the CPUex502, the memory controller ex503, the stream controller ex504, thedriving frequency control unit ex512, the configuration of the controlunit ex501 is not limited to such. For example, the signal processingunit ex507 may further include a CPU. Inclusion of another CPU in thesignal processing unit ex507 can improve the processing speed.Furthermore, as another example, the CPU ex502 may serve as or be a partof the signal processing unit ex507, and, for example, may include anaudio signal processing unit. In such a case, the control unit ex501includes the signal processing unit ex507 or the CPU ex502 including apart of the signal processing unit ex507.

The name used here is LSI, but it may also be called IC, system LSI,super LSI, or ultra LSI depending on the degree of integration.

Moreover, ways to achieve integration are not limited to the LSI, and aspecial circuit or a general purpose processor and so forth can alsoachieve the integration. Field Programmable Gate Array (FPGA) that canbe programmed after manufacturing LSIs or a reconfigurable processorthat allows re-configuration of the connection or configuration of anLSI can be used for the same purpose. Such a programmable logic devicecan typically execute the moving picture coding method and the movingpicture decoding method described in each of the embodiments, by loadingor reading, from a memory, a program included in software or firmware.

In the future, with advancement in semiconductor technology, a brand-newtechnology may replace LSI. The functional blocks can be integratedusing such a technology. The possibility is that the present disclosureis applied to biotechnology.

Embodiment 7

When video data generated in the moving picture coding method or by themoving picture coding apparatus described in each of embodiments isdecoded, compared to when video data that conforms to a conventionalstandard, such as MPEG-2, MPEG-4 AVC, and VC-1 is decoded, theprocessing amount probably increases. Thus, the LSI ex500 needs to beset to a driving frequency higher than that of the CPU ex502 to be usedwhen video data in conformity with the conventional standard is decoded.However, when the driving frequency is set higher, the power consumptionincreases.

In view of this, the moving picture decoding apparatus, such as thetelevision ex300 and the LSI ex500 is configured to determine to whichstandard the video data conforms, and switch between the drivingfrequencies according to the determined standard. FIG. 35 illustrates aconfiguration ex800 in the present embodiment. A driving frequencyswitching unit ex803 sets a driving frequency to a higher drivingfrequency when video data is generated by the moving picture codingmethod or the moving picture coding apparatus described in each ofembodiments. Then, the driving frequency switching unit ex803 instructsa decoding processing unit ex801 that executes the moving picturedecoding method described in each of embodiments to decode the videodata. When the video data conforms to the conventional standard, thedriving frequency switching unit ex803 sets a driving frequency to alower driving frequency than that of the video data generated by themoving picture coding method or the moving picture coding apparatusdescribed in each of embodiments. Then, the driving frequency switchingunit ex803 instructs the decoding processing unit ex802 that conforms tothe conventional standard to decode the video data.

More specifically, the driving frequency switching unit ex803 includesthe CPU ex502 and the driving frequency control unit ex512 in FIG. 34.Here, each of the decoding processing unit ex801 that executes themoving picture decoding method described in each of embodiments and thedecoding processing unit ex802 that conforms to the conventionalstandard corresponds to the signal processing unit ex507 in FIG. 34. TheCPU ex502 determines to which standard the video data conforms. Then,the driving frequency control unit ex512 determines a driving frequencybased on a signal from the CPU ex502. Furthermore, the signal processingunit ex507 decodes the video data based on the signal from the CPUex502. For example, the identification information described inEmbodiment 5 is probably used for identifying the video data. Theidentification information is not limited to the one described inEmbodiment 5 but may be any information as long as the informationindicates to which standard the video data conforms. For example, whenwhich standard video data conforms to can be determined based on anexternal signal for determining that the video data is used for atelevision or a disk, etc., the determination may be made based on suchan external signal. Furthermore, the CPU ex502 selects a drivingfrequency based on, for example, a look-up table in which the standardsof the video data are associated with the driving frequencies as shownin FIG. 37. The driving frequency can be selected by storing the look-uptable in the buffer ex508 and in an internal memory of an LSI, and withreference to the look-up table by the CPU ex502.

FIG. 36 illustrates steps for executing a method in the presentembodiment. First, in Step exS200, the signal processing unit ex507obtains identification information from the multiplexed data. Next, inStep exS201, the CPU ex502 determines whether or not the video data isgenerated by the coding method and the coding apparatus described ineach of embodiments, based on the identification information. When thevideo data is generated by the moving picture coding method and themoving picture coding apparatus described in each of embodiments, inStep exS202, the CPU ex502 transmits a signal for setting the drivingfrequency to a higher driving frequency to the driving frequency controlunit ex512. Then, the driving frequency control unit ex512 sets thedriving frequency to the higher driving frequency. On the other hand,when the identification information indicates that the video dataconforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1, in Step exS203, the CPU ex502 transmits a signal for setting thedriving frequency to a lower driving frequency to the driving frequencycontrol unit ex512. Then, the driving frequency control unit ex512 setsthe driving frequency to the lower driving frequency than that in thecase where the video data is generated by the moving picture codingmethod and the moving picture coding apparatus described in each ofembodiment.

Furthermore, along with the switching of the driving frequencies, thepower conservation effect can be improved by changing the voltage to beapplied to the LSI ex500 or an apparatus including the LSI ex500. Forexample, when the driving frequency is set lower, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set to a voltage lower than that in the case where the drivingfrequency is set higher.

Furthermore, when the processing amount for decoding is larger, thedriving frequency may be set higher, and when the processing amount fordecoding is smaller, the driving frequency may be set lower as themethod for setting the driving frequency. Thus, the setting method isnot limited to the ones described above. For example, when theprocessing amount for decoding video data in conformity with MPEG-4 AVCis larger than the processing amount for decoding video data generatedby the moving picture coding method and the moving picture codingapparatus described in each of embodiments, the driving frequency isprobably set in reverse order to the setting described above.

Furthermore, the method for setting the driving frequency is not limitedto the method for setting the driving frequency lower. For example, whenthe identification information indicates that the video data isgenerated by the moving picture coding method and the moving picturecoding apparatus described in each of embodiments, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set higher. When the identification information indicates thatthe video data conforms to the conventional standard, such as MPEG-2,MPEG-4 AVC, and VC-1, the voltage to be applied to the LSI ex500 or theapparatus including the LSI ex500 is probably set lower. As anotherexample, when the identification information indicates that the videodata is generated by the moving picture coding method and the movingpicture coding apparatus described in each of embodiments, the drivingof the CPU ex502 does not probably have to be suspended. When theidentification information indicates that the video data conforms to theconventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1, the drivingof the CPU ex502 is probably suspended at a given time because the CPUex502 has extra processing capacity. Even when the identificationinformation indicates that the video data is generated by the movingpicture coding method and the moving picture coding apparatus describedin each of embodiments, in the case where the CPU ex502 has extraprocessing capacity, the driving of the CPU ex502 is probably suspendedat a given time. In such a case, the suspending time is probably setshorter than that in the case where when the identification informationindicates that the video data conforms to the conventional standard,such as MPEG-2, MPEG-4 AVC, and VC-1.

Accordingly, the power conservation effect can be improved by switchingbetween the driving frequencies in accordance with the standard to whichthe video data conforms. Furthermore, when the LSI ex500 or theapparatus including the LSI ex500 is driven using a battery, the batterylife can be extended with the power conservation effect.

Embodiment 8

There are cases where a plurality of video data that conforms todifferent standards, is provided to the devices and systems, such as atelevision and a cellular phone. In order to enable decoding theplurality of video data that conforms to the different standards, thesignal processing unit ex507 of the LSI ex500 needs to conform to thedifferent standards. However, increase in the scale of the circuit ofthe LSI ex500 and increase in the cost arise with the individual use ofthe signal processing units ex507 that conform to the respectivestandards.

In view of this, what is conceived is a configuration in which thedecoding processing unit for implementing the moving picture decodingmethod described in each of embodiments and the decoding processing unitthat conforms to the conventional standard, such as MPEG-2, MPEG-4 AVC,and VC-1 are partly shared. Ex900 in FIG. 38A shows an example of theconfiguration. For example, the moving picture decoding method describedin each of embodiments and the moving picture decoding method thatconforms to MPEG-4 AVC have, partly in common, the details ofprocessing, such as entropy coding, inverse quantization, deblockingfiltering, and motion compensated prediction. The details of processingto be shared probably include use of a decoding processing unit ex902that conforms to MPEG-4 AVC. In contrast, a dedicated decodingprocessing unit ex901 is probably used for other processing which isunique to an aspect of the present disclosure and does not conform toMPEG-4 AVC. Since the aspect of the present disclosure is characterizedby partitioning of a picture in particular, for example, the dedicateddecoding processing unit ex901 is used for the partitioning of apicture. Otherwise, the decoding processing unit is probably shared forone of the inverse quantization, entropy decoding, deblocking filtering,and motion compensation, or all of the processing. The decodingprocessing unit for implementing the moving picture decoding methoddescribed in each of embodiments may be shared for the processing to beshared, and a dedicated decoding processing unit may be used forprocessing unique to that of MPEG-4 AVC.

Furthermore, ex1000 in FIG. 38B shows another example in that processingis partly shared. This example uses a configuration including adedicated decoding processing unit ex1001 that supports the processingunique to an aspect of the present disclosure, a dedicated decodingprocessing unit ex1002 that supports the processing unique to anotherconventional standard, and a decoding processing unit ex1003 thatsupports processing to be shared between the moving picture decodingmethod according to the aspect of the present disclosure and theconventional moving picture decoding method. Here, the dedicateddecoding processing units ex1001 and ex1002 are not necessarilyspecialized for the processing according to the aspect of the presentdisclosure and the processing of the conventional standard,respectively, and may be the ones capable of implementing generalprocessing. Furthermore, the configuration of the present embodiment canbe implemented by the LSI ex500.

As such, reducing the scale of the circuit of an LSI and reducing thecost are possible by sharing the decoding processing unit for theprocessing to be shared between the moving picture decoding methodaccording to the aspect of the present disclosure and the moving picturedecoding method in conformity with the conventional standard.

INDUSTRIAL APPLICABILITY

The present disclosure can be applied to an image coding method, animage decoding method, an image coding apparatus, and an image decodingapparatus. In addition, the present disclosure can be used forhigh-resolution information display devices or image-capturing deviceswhich include image coding apparatuses, such as a television, a digitalvideo recorder, a car navigation system, a cellular phone, a digitalstill camera, and a digital video camera.

The invention claimed is:
 1. An image decoding method for decoding abitstream including a coded signal resulting from coding a plurality ofslices into which an image is partitioned and each of which includes aplurality of coding units, the method comprising decoding the codedsignal, wherein each of the slices is either a normal slice having, in aslice header, information used for another slice or a dependent slicewhich is decoded using information included in a slice header of anotherslice, the image includes a plurality of rows each of which includes twoor more of the coding units, and when the normal slice starts at aposition other than a beginning of a first row, a second row immediatelyfollowing the first row does not start with the dependent slice, whereinin the decoding, arithmetic decoding of the second row is initializedusing a context obtained after arithmetic decoding of one of the codingunits that is located second in the first row.
 2. An image decodingapparatus which decodes a bitstream including a coded signal resultingfrom coding a plurality of slices into which an image is partitioned andeach of which includes a plurality of coding units, the apparatuscomprising a decoding unit configured to decode the coded signal,wherein each of the slices is either a normal slice having, in a sliceheader, information used for another slice or a dependent slice which isdecoded using information included in a slice header of another slice,the image includes a plurality of rows each of which includes two ormore of the coding units, and when the normal slice starts at a positionother than a beginning of a first row, a second row immediatelyfollowing the first row does not start with the dependent slice, whereinthe decoding unit is configured to initialize arithmetic decoding of thesecond row by using a context obtained after arithmetic decoding of oneof the coding units that is located second in the first row.